Progress 10/01/01 to 09/30/04
Outputs
The overall goal of this project was to determine the area fished by a lobster trap and we achieved this goal. During the 3-year project we tracked the movements of 32 lobsters using ultrasonic telemetry. The lobsters studied ranged in size from 65 to 90 mm in carapace length and data was collected from them for periods ranging from 24 hours to > 7 days. The lobsters used were captured within a large 50m X 50m enclosure in a cove along the coast of NH, equipped with an ultrasonic transmitter, and then released within the enclosure. Positional data (x,y coordinates ) were collected for each lobster, every 5 min, using an array of three buoys equipped with hydrophones and a radio transmitter to communicate with the shore station. These data were used to determine their home range and daily patterns of locomotion. After collecting control data for at least 3 days, a lobster trap equipped with a time-lapse video system was deployed within the enclosure to study the
influence of the trap on lobster movements. We found that, while lobsters had a tendency to move the greatest distances at night, they were also quite active during the day. Home ranges were calculated using the fixed kernal method and the Animal Movement Extension for ArcView. They ranged from 100 to 3000 square meters and there was no correlation between animal size and home range size. Only 14 of 25 lobsters tracked with a trap in the enclosure approached the trap when it was deployed and typically they turned toward the odor plume emanating from the bait at distances less than 11 meters. By taking into account the mean home range for lobsters (1000 square meters) and the area of bait attraction (380 square meters), we were able to estimate the area fished by a trap to be approximately 2642 square meters. By knowing the area fished by a trap, the typical catch per trap haul and the efficiency of the trap, it was possible to estimate the population within the enclosure. In a
preliminary comparison between the estimate and the actual density the model was surprisingly accurate.
Impacts
So far we have used ultrasonic telemetry to determine the area of bait attraction around a lobster trap, the home range of a lobster, and the area fished by a trap. This is the first time any of these discoveries have been made using the American lobster and this significantly enhances our knowledge of this valuable species. We plan to use the data obtained to better estimate the abundance of lobsters, and thus determine if fishing is having an impact on the lobster population.
Publications
- No publications reported this period
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Progress 10/01/02 to 09/30/03
Outputs
The second year of our three-year project was very successful, both in terms of data collection and analysis. In the fall of 2003 one of the graduate students involved in the project attended a GIS course to learn how to use an Animal Movement Analysis Extension for Arcview to analyze the tracking data we had obtained using ultrasonic telemetry. During the subsequent winter (2002 to 2003) we used this program to plot all of our data from the summer of 2002. We were able to plot the home range of each lobster tracked, for each day they were tracked. The results of this analysis was used as part of the Masters Thesis of a student who just graduated, Walter Golet. Out of the 35 lobsters we tracked in 2002, 25 yielded data that was acceptable for further analysis. On average the daily home range of these lobsters was 1052 square meters (range 166 to 3000 square meters). There was no relationship between lobster size and home range, however, regardless of size, lobsters
that traveled the most in a given day also had the largest home range. We were also able to use a fine-scale analysis of lobster movements to determine the area of bait attraction. This analysis revealed that lobsters that passed closer than 11m from a trap were able to detect the bait in the trap. We also determined that 60% of the lobsters that passed within 11m, actually approached the trap; the rest walked past and were not attracted by the bait. By combining our data concerning the area of bait attraction with our calculations of lobster home range, we were able to estimate the area fished by a trap. This value turned out to be 2642 square meters. These data are also a part of a graduate student thesis and he presented this information at two National meetings in 2003. During the summer of 2003 we continued our field studies and we were able to obtain additional tracking data from 24 more lobsters. During the fall and winter of the third year of the project we plan to fully
analyze those data, combine it with our field data from 2002, and thus have sufficient sample size for publication of 3 manuscripts on the subject in the spring of 2004. At that point we will have accomplished 3 of our 4 objectives for the project. During the remainder of the year we will obtain the data necessary to complete the final objective of creating a comprehensive model that will estimate lobster density based upon catch.
Impacts
So far we have used ultrasonic telemetry to determine the area of bait attraction around a lobster trap, the home range of a lobster, and the area fished by a trap. This is the first time any of these discoveries have been made using the American lobster and this significantly enhances our knowledge of this valuable species. We plan to use the data obtained to better estimate the abundance of lobsters, and thus determine if fishing is having an impact on the lobster population.
Publications
- Golet, W.J. 2003. Small-scale movements and interactions of the lobster Homarus americanus with traps. Master's Thesis. University of New Hampshire, Durham, New Hampshire. pp. 102.
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Progress 10/01/01 to 09/30/02
Outputs
The overall goal of this project is to develop an improved method for measuring the area fished by a trap so that catch data can be translated into a calculation of the actual abundance of lobsters on the bottom. In spring of 2002 we moved our study site from the waters offshore from the Wallis Sands State Beach (Rye, NH) to a cove adjacent to the Portsmouth Coast Guard Station, in Newcastle, NH. In this cove we constructed a 50 meter by 50 meter underwater enclosure. The enclosure was designed to prevent lobsters equipped with ultrasonic transmitters from moving beyond the limits of the VEMCO tracking system we deployed. The VEMCO tracking system uses 3 buoys to triangulate the position of lobsters equipped with ultrasonic transmitters, every 2 minutes, with an accuracy of approximately 1 meter. The average depth in the enclosure was 8 meters and the bottom type included sand, eelgrass and small cobble areas. With the cooperation of local fishermen, the only traps
fished in and around the site were our own. During 14 weeks, from the end of June to the beginning of October, we successfully tracked 35 lobsters ranging in size from 65 to 87mm in carapace length. A total of 18 males and 17 females were tracked for a total of 170 lobster days (4-7 days each). Typically, 4 lobsters were tracked during each trial. After collecting control data for 2-3 days, a baited trap equipped with a pinger and video camera were deployed inside the pen. The trap was pulled the following day, rebaited and deployed again for a total of three days. Four different lobsters entered traps on separate occasions and several more approached the trap, but never entered. In general, lobsters were attracted to the trap from distances of approximately 10 meters, depending on current direction. Further data is required before final conclusions concerning area of bait attraction can be reported. The data collected can also be used to calculate home-range/foraging area of
different size class lobsters, determine daily periods of activity, and their average rate of locomotion. By combining these different types of measurements we will calculate the area fished by a trap, as it pertains to different size classes of lobsters. Our data analyses have been delayed because we are perfecting a method for improving the accuracy of the data by correcting for buoy movement using the program Matlab. We anticipate completing our analysis of the 2002 data by February. Currently, we have completed objectives one and two and will work towards completing objective number four as soon as all the data has been analyzed.
Impacts
Completion of this project will provide the groundwork necessary to formulate a model capable of estimating the abundance of lobsters on the bottom. To date, no such model exists because many aspects of lobster behavior in the field have yet to be determined. This project will provide information needed to create a more accurate model that is capable of tracking trends in the fishery. This information is vital for ensuring the sustainability of such a valuable commercial fishery.
Publications
- No publications reported this period
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Progress 10/01/00 to 09/30/01
Outputs
The overall goal of this project is to develop an improved method for measuring the area fished by a lobster trap so that catch data can be translated into the actual abundance of lobsters on the bottom. Our major accomplishment this past year was working out all the tracking instrumentation and methodology. Due to numerous unpredictable problems we were only able to intermittently track four animals for a three-week period. Currently we are in the process of analyzing the data files we generated with the VEMCO tracking system, using MatLab software. Three of the four briefly occupied a shelter within the study site and then moved offshore, outside the area covered by the tracking system. Most excursions from the shelters took place at night with the animals returning close to their shelters before dawn. We are in the process of calculating each animal's home range and average rate of locomotion. Our greatest problem this past year was that tagged lobsters moved out
of our study area. Our solution to this problem is to enclose the study site with an underwater fence. This fence will be made of vinyl coated twelve-gauge trap wire with one and a half by one and a half inch mesh. We hope to enclose the majority of our study site, which is approximately ten thousand square meters. This area is large enough to allow us to make most of our calculations of area fished, home range, etc., while at the same time preventing lobsters from moving our of the range of our tracking instrumentation. Another significant problem is the VEMCO software. It is a very old DOS-based system, which can be tedious to use and the data generated is hard to analyze. However, VEMCO is now in the test phase for their new Windows version software. This software should be available in the spring. This will allow us more flexibility for data analysis as well as improved triangulation accuracy. During the winter we will continue to analyze our data files from last field season to
begin meeting Objective One. We will test our underwater enclosure system at the Coastal Marine Lab to ensure that animals are not capable of escaping. If successful we will start construction on site in late April or early May. This enclosure will give us the ability to retrieve tags after the lobsters have been tracked. We hope to track approximately twenty lobsters over the summer, each for a period of about one week. We also plan to deploy a lobster trap inside the study area so we can compare their movements before and after the trap is present. Placing a pinger on the trap will allow us to follow the lobster movements in relation to the trap at all times. If the animal enters the trap we will be able to determine how far it traveled to get to the trap and thus the area fished by a trap.
Impacts
The greatest impact of our work will be to provide knowledge about the foraging area and home range of the American lobster. By combining this information with data concerning the area fished by a trap, we should be able to more accurately estimate the density of lobsters on the bottom, in terms of lobsters per square meter, more accurately than with other methods. This data will greatly aid in the effective management of this valuable marine resource.
Publications
- No publications reported this period
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Progress 01/01/00 to 12/31/00
Outputs
In the third year of this project we successfully completed 4 out of the 5 objectives listed in our proposal. These data have formed the basis for 3 presentations at International meetings in the last year, 1 manuscript that is in press, two manuscripts that are currently in preparation, two new grants that are currently pending, two graduate student theses that are in preparation, and two undergraduate senior projects. A good summary of our findings can be viewed on the following web site:http://zoology.unh.edu/faculty/win/win.html, where a copy of the poster presented at the International Lobster Conference is posted. We have also produced a video that we are distributing to those who request it. The essential findings of our study are summarized below. The three most significant lobster predators we observed were lobsters, crabs and skates (85, 60 and 27 attacks/99 hrs of analyzed video respectively). Striped bass and other fish were often observed approaching
tethered lobsters, but they rarely attacked them. Laboratory studies confirmed that adult lobsters will attack and eat smaller lobsters, even when they are not tethered. Most of the skates observed in the study area were large enough to consume juvenile lobsters. The average disc size of the skates measured during trawl surveys was 234.7 mm and the average size observed approaching lobsters in the time-lapse videos was 194.7 mm. The mean size of lobsters in the study area was 59.9 mm in carapace length and the mean size we tethered for predation studies was 39.7 mm CL. Lobster parts were found in the stomach contents of 2 of 12 skates examined, confirming that skate predation on lobsters occurs under normal circumstances in our study site. However, while skates are abundant in N.H. coastal waters the density (1-3 skates/1000 meters squared) does not appear to be sufficient to have a significant impact on lobster abundance (10-150 lobsters/1000 meters squared). While the lobster
density gradually increased from June through September, and then decreased in October, changes in the density of skates paralleled this curve and thus did not account for changes in the abundance of lobsters. We were unable to get skates to feed well in the laboratory so we were unable to quantify the size range of lobsters that skates of a given size preferred to eat. In conclusion, this project was extremely successful. We answered the questions we set out to examine and we have begun to share our findings in a variety of different forums.
Impacts
The greatest impact of this work was to demonstrate that other crustaceans and skates are the primary lobster predators along the coast of N.H. Although striped bass and various large fish do eat lobsters, it is a relatively rare occurrence, based on our study. Overall, it does not appear as if fish predation has a major impact on the abundance of lobsters in our study area.
Publications
- No publications reported this period
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Progress 01/01/99 to 12/31/99
Outputs
During the summer of 1998 we focused most of our attention on Objectives 1, 3 and 4. We developed a method for obtaining long-term video recordings of tethered lobsters so we could determine the primary fish predators. Our data indicate that skates (Raja ocellata and R. erinacea) are by far the most common lobster predators along the N.H. coastline, as least in sandy habitats. This is our most significant finding to date, we have presented it at several National Meetings and at least 2 publications on this subject are currently in preparation. This past summer, 1999, we concentrated most of our efforts on Objectives 2,3 and 5. A primary goal was to quantify the abundance of skates along the N.H. coast and examine their stomach contents for evidence that they recently consumed a lobster. We completed a total of 19 otter trawls, from July 16th to August 19th. A total of 31 skates (15 Raja ocellata and 16 R. erinacea) were caught, yielding a catch per trawl of 1.63
skates. Sizes ranged from 235 to 505 mm in total length (TL). Lobster traps were fished simultaneously in the same area, and lobsters taken in trawls were also quantified. We now have data on lobsters abundance between May and October, in both 1998 and 1999 and it is clear that the population is very sparse in May and June, peaks from July -September and then declines in October. Our fish sampling only took place during July and August in 1999 so no conclusions can be drawn at this time concerning the relationship between skate abundance and the local lobster population (Objective 2). Next year sampling will extend from May-October. Stomach content analyses revealed small crustaceans as the major food item; with clear evidence of lobster parts in two skates (315mm and 480mm TL, Obj. 3). To further asses the abundance and types of predatory fish in this study area, a 50m long, 6" mesh size, monofilament, bottom tending gillnet was deployed for 24 hrs, on 6 occasions. As in 1998,
relatively few fish were caught. Of these, there were 5 potential lobster predators; 2 skates, 2 strippers and 1 sea raven. There were no distinguishable food items in their gut, which is not unusual with 24 hour sampling. So far, our attempts to get skates to feed on lobsters in the laboratory have not been successful, so Objective 5 will have to be addressed using further analyses of videotapes obtained in the field.
Impacts
The most important finding of this project to date is the recognition that skates are the most signficant lobster predator in areas with a sandy bottom along the coast of New Hampshire. Previously the influence of skates on lobsters populations was not fully appreciated. Another important impact of this project was the development of a sophisticated mechanism for obtaining time-lapse video recordings in the marine habitat. We have received many requests from other scientists who want to adopt our system for their investigations.
Publications
- No publications reported this period
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Progress 01/01/98 to 12/31/98
Outputs
During our first summer of research on this project we focussed most of our attention on Objectives 1, 3 and 4. A 50m long, 6" mesh size, monofilament, bottom tending gillnet was deployed on 3 occasions in August. Relatively few fish were caught, and most were not potential lobster predators (e.g. mackerel). None of the potentially predatory species captured (skates and sea ravens) contained lobsters in their gut. The few fish captured precludes us from reaching any conclusions on this aspect of the study. Enhanced sampling planned for next summer should allow us to determine how important these, and other, finfish species are as lobster predators. Most of our efforts last summer were devoted to video analysis of lobster predation. First we developed a system capable of collecting 24-48 hour time-lapsed underwater videos. Then we used the system to videotape tethered lobsters being attacked by predators. We recorded more than 100 attacks of lobsters (25-50 mm in
carapace length) by skates. Although we observed crabs, striped bass, and other potential predators in the area, only skates, and 3 adult lobsters, attacked and in many cases, consumed, the tethered lobsters. Based on these observation we conclude that in this region we should focus most of our attention on examining the influence of skates on lobsters populations.
Impacts
(N/A)
Publications
- No publications reported this period
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Progress 01/01/97 to 12/31/97
Outputs
The overall goal of this project was to determine the role of seagrass beds as a habitat for lobsters. SCUBA surveys revealed a greater abundance of lobsters in seagrass beds, in comparison with adjacent sandy substrate, while surveys using both traditional traps and traps modified to catch small lobsters, revealed no difference in density. This is likely due to lobsters foraging outside of seagrass meadows at night, and then getting captured in traps. The primary goal of the final year of investigation was to determine if seagrass beds served as a refuge from predation. Lobsters (n=152) ranging in size from 30 to 85 mmCL, were tethered to the bottom using 2 ft. steel leaders, either in seagrass beds or on adjacent sandy substrate. Typically, 3-6 lobsters were tethered in each site, 5 meters apart. After 24 hrs they were checked by SCUBA to determine which ones were eaten. Two major findings resulted from this experiment. First, there was no statistically significant
difference in the mortality rate of lobsters in, and out of, seagrass beds. Second, while there is heavy predation (70% mortality) on lobsters smaller than 50 mmCL, those in larger size classes were rarely eaten (15%). These findings suggest that the animals which prey upon lobsters along the N.H. are equally effective in both seagrass meadows and sand. Therefore, it is likely that the higher abundance of lobsters in seagrass is more related to lobsters seeking prey, than avoiding predators.
Impacts
(N/A)
Publications
- CROSSIN, G.T., S. A. AL-AYOUB, S.H. JURY, W.H. HOWELL AND W.H. WATSON III. 1998. Behavioral thermoregulation in the American lobster, Homarus americanus. J. Exp. Biol. 201: 365-374.
- DUFORT, C. 1997. Salinity detection by the American lobster, Homarus americanus. M.S. Thesis. University of New Hampshire, Durham, N.H. 46 pp.
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Progress 01/01/96 to 12/30/96
Outputs
The major goal of this project is to determine the importance of eelgrass beds as a lobster habitat. We continued to survey eelgrass beds (E), and adjacent control sand sites (S), using traditional lobster traps and SCUBA. In traps, we caught a total of 293 lobsters in our estuary study site, and 247 at the coast. The catch/trap haul was greater in S areas than in the E (Est=1.68 vs. 1.27; Coast=1.57 vs. 1.05), and the average size of the lobsters in E vs. S was comparable. In contrast, with SCUBA surveys 93% of the lobsters were found in eelgrass, both our estuarine and coastal sites. This suggests that lobsters reside in eelgrass beds, but their foraging range extends into adjacent sediment areas. To determine if lobsters use eelgrass beds to avoid predators we tethered a total of 62 lobsters in E and S areas. Predation was high on lobsters smaller than 45 mmCL, with more than 60% of the animals eaten after 24 hrs. In contrast, less than 20% of the lobsters >55 mm
CL suffered predation. As predicted, animals in E were eaten less (23%), than lobsters tethered in the S (33%). We also continued our investigations of how lobsters use behavioral and physiological mechanisms to survive in an estuarine habitat. We determined that exposure to low salinity water is sufficient to cause an increase in Na+/K+pump activity, suggesting that differences in the osmoregulatory capabilities of coastal and estuarine lobsters are due primarily to acclimation.
Impacts
(N/A)
Publications
- ROCKEL, C. 1996. A comparison of osmoregulatory abilities in estuarine and coastal lobsters, Homarus americanus. Master's Thesis, UNH, Durham, N.H.
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Progress 01/01/95 to 12/30/95
Outputs
This was the second year of a 3 year project. Our main goal is to determine the extent to which lobsters utilize eelgrass as a habitat. We fished lobster traps and conducted diver surveys in both estuarine and coastal eelgrass beds, as well as in adjacent control sites with a sandy substrate. As expected, we found a greater number of lobsters in all coastal sites. More importantly, as in 1994, our SCUBA surveys found that there were more lobsters in the eelgrass beds than in adjacent sandy areas and this difference was more pronounced at the coast than in the estuary. In contrast, our traps caught more lobsters in the sandy sites than in the eelgrass. Our interpretation of these findings is that the larger lobsters, which are most frequently caught in traps, do not require the shelter offered by the eelgrass beds and they tend to forage for food over a much larger area, including out into the open sand. This hypothesis is support by the finding that on average, the
lobsters found in the eelgrass habitats were smaller. Thus, eelgrass habitats may function as important nursery areas for smaller, less mobile, and more vulnerable lobsters. Next year we will used tethering studies to determine if the smaller lobsters inhabitat eelgrass beds because they provide a refuge from predators.
Impacts
(N/A)
Publications
- NO PUBLICATIONS REPORTED THIS PERIOD.
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Progress 01/01/94 to 12/30/94
Outputs
In the past year we completed two projects and initiated a third. In the first project we found lobster density correlated most closely with substrate differences between sites. This strongly suggests that spatial differences in substrate types, which provide inherently different numbers and sizes of shelters, strongly influence spatial differences in lobster abundance. Except for the upper estuary, prey abundance and variety was high at all sites, and lobsters did not appear to be food-limited, suggesting prey availability does not have as great an influence on lobster distribution as substrate type. In the second project we demonstrated that soft-shelled lobsters are quite vulnerable to predation in comparison to hard-shelled animals. We also found that this risk was considerably reduced if shelters were provided; adding further support to the theory that shelter availability dictates lobster abundance. The aforementioned results motivated us to examine eelgrass beds
as possible lobster habitats. In our first year of this study we found a much higher abundance of lobsters in eelgrass beds than in adjacent sandy areas, demonstrating it is a preferred habitat. In 1995 we will determine if this habitat is preferred because it provides a refuge from predators.
Impacts
(N/A)
Publications
- BECKER, C., HOWELL, W.H. AND WATSON, W.H. 1994. Dietary preferences of the estuarine lobsters. Presented at the Benthic Ecology Meetings.
- BECKER, C. 1994. The influence of prey availability and habitat structure on the distribution of lobsters (Homarus americanus) in the Great Bay Estuary, MS Thesis, Dept. of Zoology, Univ. New Hampshire.
- JURY,S.,HOWELL,W.H. AND WATSON,W.H. 1995. Lobster movements in response to a Hurricane. Mar. Prog. Series (In Press).
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Progress 01/01/93 to 12/30/93
Outputs
In the past year we have focused our attention on 3 issues: food availability, dietary preferences, and the relationship between shelter availability and the vulnerability of lobsters to predation. We found that while the abundance of potential lobster prey items (cabs, snails, polychaetes, etc.) was comparable in both estuarine and coastal waters, the relative number of each prey species varied considerably from site to site. Examination of lobster gut contents revealed that their diet was not a direct manifestation of the relative numbers of prey in their immediate habitat. This may reflect either a high preference for certain prey items, or difficulty acquiring certain types of prey in complex habitats with numerous prey refuges. It is thought that lobster populations are limited by the availability of shelters. Most research has focused on juvenile stages because large lobsters are thought to be invulnerable to predation. However, we found that just after molting,
soft-shelled mature lobsters are subjected to heavy predation, especially if they are not in a shelter. This suggests that shelter availability has an impact on the composition of lobster populations during all life history stages. Next year we plan to focus our attention primarily on shelter-related issues. Our goals are to extend the work cited above and to determine the extent to which the distribution of lobsters is related to the relative availability of shelters.
Impacts
(N/A)
Publications
- PUIG-SUARI, N. 1993. The effect of shelter on the vulnerability of soft-shell lobsters (Homarus americanus) to predation. M.S. Thesis, University of New Hampshire, 36 pp.
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Progress 01/01/92 to 12/30/92
Outputs
In our first year of research, we began field work in 3 sites in the Great Bay Estuary. We have compiled the necessary information to address our first three objectives, and also collected preliminary information for the remaining objectives. The types and amounts of available prey items, lobster abundances, and trap densities at each site were estimated from July through November by conducting bi-weekly transects using SCUBA. To estimate densities of smaller prey, and prey that burrow in the sediment, random quadrat counts and benthic core samples were collected. A total of 10 lobsters per site each month were dissected, and gut contents were preserved for later analysis. Results of transect and gut content data will indicate potential prey preferences displayed by lobsters in the estuary. While SCUBA diving at each site, general substratum descriptions were recorded to correlate changes in lobster abundances with substratum variation. During all SCUBA transects,
occupied lobster shelters were categorized as rock, depression, or other structure present in the habitat (logs, tires...). These data, along with data from ongoing studies, are currently being analyzed to determine the most important factors controlling the abundance of lobsters in the Great Bay Estuary.
Impacts
(N/A)
Publications
- No publications reported this period.
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Progress 01/01/91 to 12/30/91
Outputs
In 1991 we caught, measured, sexed, molt-staged, tagged, and released about 5,400 lobsters in the estuarine and coastal waters of New Hampshire. Of these, about 500 were recaptured. Analyses of these data, along with similar data collected in 1989 and 1990, indicates that the lobster population structure differs between locations. Included are differences in catch per effort, mean size, sex ratio, and molt timing and frequency. Tag-recapture data indicates that most lobsters tend to move down the estuary in the fall and back up the estuary in late spring or early summer. This was confirmed by the tracking of an additional 21 lobsters fitted with individually coded sonar transmitters. All of those fitted and tracked before July moved up the estuary, while all fitted and tracked in the fall moved down the estuary. Most displayed little movement during the summer months. These data strongly suggest that estuarine and coastal lobsters mix in space and time, and therefore
should be treated as one population for management purposes. Several laboratory experiments were conducted to examine the behavioral responses of lobsters to decreases in salinity. These experiments indicated that lobsters can detect changes in salinity, that locomotor responses to reduced salinity differ between males and females, and that lobsters behaviorally avoid low salinity areas. These experiments, once completed, will help us explain observed spatial differences in sex ratios, and the underlying reasons for observed seasonal movements.
Impacts
(N/A)
Publications
- No publications reported this period.
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Progress 01/01/90 to 12/30/90
Outputs
From April to December of 1990 we tagged and released about 4,700 lobsters in the Great Bay Estuary. Approximately 900 of these were recaptured and reported to us by commercial lobstermen. Analysis of data from these recaptured animals is not yet complete, but a preliminary examination indicated that our second year's data is consistent with the trends reported after our first year; lobsters move into the estuary in the summer, and down the estuary in the fall. Thus, it appears that there is considerable mixing between estuarine and coastal populations. Thirteen lobsters were fited with individually coded sonar transmitters, and tracked in the estuary for varying periods of time. In addition, we continued to track animals fitted with sonar tags the previous fall. All sonar tagged animals moved up the estuary in May and June and down the estuary from August to November. While there was a correlation between lobster movements and seasonal changes in temperature
and salinity, it is still not clear what cues are being used to initiate and guide movements. To characterize the structure of the estuarine lobster population, we sampled 5 different locations with traps. As in 1989, we found differences in size, sex ratio, and abundance of lobsters at different locations. The most striking finding was that the upper estuary is dominated by large, male lobsters.
Impacts
(N/A)
Publications
- VETROVS, A. 1989. The distribution of lobsters (Homarus americanus) in the Great Bay Estuary. Masters Thesis. University of New Hampshire.
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Progress 01/01/89 to 12/30/89
Outputs
During the first year of this project, we tagged and released 4,200 lobsters in the Great Bay Estuary and the Isles of Shoals. Approximately 800 of the tagged lobsters have been recaptured. Our analysis of movement data from these recaptured animals suggests that during the summer and fall lobsters move down the estuary, towards the Gulf of Maine. Data from this winter and spring will help us to confirm our hypothesis that during the late spring, after the freshwater run-off, lobsters move back up into the estuary. Some of the animals tagged and released at the Isles of Shoals moved toward the coast, but none were recaptured in the estuary. Some lobsters tagged in the estuary were recaptured 5-10 miles offshore, or along the coast of Massachusetts, to the south, but none were recaptured at the Isles of Shoals. Eleven lobsters were fitted with individually coded sonar transmitters, and tracked in the estuary for varying periods of time. Data from these animals was
consistent with the movement patterns extrapolated from the tag/recapture aspect of the study. In order to characterize the structure of the lobster population in the estuary, we sampled at 5 different locations, using traditional lobster pots. We found differences in the size, sex, and catch per unit effort in different regions of the estuary, ranging from the coast (Coastal Marine Lab) to the middle of Great Bay, 14 miles from the coast.
Impacts
(N/A)
Publications
- NO PUBLICATIONS REPORTED THIS PERIOD.
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