Performing Department
Forest Resources and Conservation
Non Technical Summary
This project will investigate the basic life history, ecology, and population dynamics of coastal fishes important to both recreational and commercial fisheries, as well as those important to sustainable ecosystems. Components of the project will focus on age and growth estimates for a variety of fish species, and estimates of mortality, both from natural causes and from catch and release mortality due to discarding of fish based on current fishing regulations. Basic reproductive information for a variety of species will also be a major aspect of the project, including defining the spawning season duration, the size and ages of fish spawning and when they start to spawn, and their egg production during each spawning event. Another major component of the project will be to assess the impacts of ecosystem perturbations on fishes and their habitats, whether from dredging of sand shoals or oil spills. The abundance and diversity of the fish assemblages potentially impacted from environmental perturbations will be assessed relative to pre-impact time periods and/or reference areas.
Animal Health Component
0%
Research Effort Categories
Basic
0%
Applied
100%
Developmental
0%
Goals / Objectives
ObjectivesEstimate basic population parameters of fishes that are commercially, recreationally, or ecologically important to fisheries or conservation, including those parameters relevant to age and growth, reproduction, and mortality;Determine the trophic dynamics of fishes and marine ecosystems, including the ecological relationships among fishes and fish assemblages;Examine factors affecting sustainability of fisheries, including environmental perturbations and management regulations.
Project Methods
As part of an umbrella document for planned research, these procedures are meant to give guidance but will be modified to suite specific objectives of any given research study or management requirement.1. Basic population parameters of fishes that are commercially, recreationally, or ecologically important to fisheries or conservation, including those relevant to age and growth, reproduction, and mortalityA. Age and GrowthFishes will be collected by fishery-dependent and fishery-independent sampling, depending on the species. For ageing, sampling will be done for all size ranges and sexes on a monthly basis in most circumstances to account for size- and sex-specific differences. All fish will be measured for total and fork lengths, weighed, and gender determined by internal examination. Sagittal otoliths will be removed for ageing. Fin rays will be removed when necessary for comparative ageing studies.i. Methods of Age DeterminationFish will be aged primarily using sagittal otoliths and, secondarily, dorsal fin-rays or spines. Sagittal otoliths will be prepared for ageing using primarily a thin-sectioning method. Cross-sections of the basal section of the rays or spines will be used to age fish non-lethally.After establishing preliminary ageing criteria, all ageing structures will be read at least twice by independent readers. Between-reader precision (i.e., reproducibility) of age estimates will be determined using the coefficient of variation and average percent error. The concordance correlation coefficient will also be estimated to determine the deviation of paired ages from a 1:1 relationship.Ages determined using sectioned otoliths, fin-rays, and fin spines will be compared by determining the percent agreement among the ageing methods. Since more than two ageing structures are being compared, the sectioned otolith ages will act as the reference for the comparison. These comparisons will be visualized by plotting the fin ray/spine ages as a function of sectioned-otolith age. Tests of symmetry will be done to check for biases in aging. Reference sets will be developed and process control of aging will be conducted in concert with regional state and federal aging laboratories.ii. Validation of Age Determination through Marginal-increment AnalysisMarginal-increments of toliths and fin rays/spines will be measured using a microscopic digital imaging system. Periodicity in the pattern of marginal-increment development will be calculated as the index of completion. The index of completion will be plotted as a function of the month of the year to determine the periodicity.iii. Growth modelsAge and growth of males and females will be estimated by fitting growth models (i.e., von Bertalanffy), to length/age data, and weight/age data. Back-calculated lengths-at-age will be determined for most species aged using the body proportional method. Differences in growth curves between males and females, between regions, and between gears will be determined using appropriate statistical methods.B. ReproductionGonads will be weighed and subsampled for histological examination of maturity. Ovaries and testes will be staged by growth phases to determine maturity and spawning conditions.Spawning periodicity will be determined by calculating the frequency of occurrence of each ovarian and testicular stage on a monthly basis. In addition, reproductive timing and gonadal condition will be examined using monthly changes in gonad mass.Sexual maturity of males and females will be derived by modeling the proportion of mature fish over the range in age and size. Fecundity will be assessed by estimating batch fecundity and spawning frequency. Batch fecundity will be estimated by enumerating the number of hydrated oocytes (or other biomarker for imminent spawning) present in a sample of known weight. Spawning frequency will be calculated as the proportion of spawning females (i.e., hydrated eggs present) in the population in relation to the total number of mature females. The relationship between fecundity and fish length will be examined using a power function.C. MortalityCatch-curves will be constructed and total instantaneous mortality (Z) will then be estimated by the slope of a linear regression fit to the descending right limb of the catch-curve. Differences in Z among groups (i.e., female and male) will be tested using analysis of covariance.2. Trophic dynamics of fishes and marine ecosystems, including the ecological relationships among fishes and fish assemblagesTo estimate food consumption, fish will be collected throughout the seasons and on a diel basis (day/night) to determine composition of their diet. Importance of prey will be estimated using percent occurrence, numerical abundance, reconstructed biomass, and reconstructed gross energy. Differences in seasonal food consumption, on a biomass or gross energy basis, will be modeled using Analysis of Covariance (ANCOVA).Diet composition and food consumption will be related to the availability of prey in the environment. Absolute prey abundance in appropriate coastal habitats will be assessed using trawling transects. The relationship between the availability of prey in the environment and the occurrence of the prey in the diet will be compared using preference and availability.Fish sampled for age and growth, feeding ecology, and reproductive characteristics will be processed to determine the seasonal cycle of lipid stores. Tissues samples will be collected from the muscle mass, liver, and gonad of each fish and analyzed for % moisture and energy density using a calorimeter. A relative fat index (RFI) will also be used to differentiate changes in lipid stores between mature and immature fish and seasons. Relative energetic contributions to formation of gonads will be examined relative to the body mass of the fish as a function of sex and maturity using ANCOVAs.3. Factors affecting sustainability of fisheries, including environmental perturbations and management For catch and release mortality, spatial coverage will be based on the major distribution of recreational fisheries for each species. Fish will be caught using hook-and-line gear while fishing from charterboats and headboats, and during fisheries-independent sampling. Prior to release, all fish will be measured for maximum total length, weighed, and tagged to allow long-term, residual effects of release mortality to be assessed.All fish captured will be examined immediately upon retrieval and assessed as being alive or dead to estimate immediate (acute) mortality. Dead individuals will be retained on ice for necropsy to determine external and internal index of damage due to barotrauma. Fish that are alive on retrieval of the gear will alternately be given a release treatment (i.e., control, vented only, or released using one of the descending devices). Recaptures will be analyzed based on treatment method, depth of initial capture, and season.To assess effects of sand dredging on fish communities, a stratified random sampling framework will be used to collect trawl samples from the ridge and swale components of three shoals (dredged and two reference shoals), seasonally, and over a 5-year period. Fish species composition and biomass, as well as physical attributes of the shoals (e.g., type of sediment, temperature), will be compared using multivariate analyses on a pre-dredge versus post-dredge period, as well as on a seasonal and annual basis. Trophic dynamics of the shoals will be determined using both stomach content analysis of the major fish species and isotope analysis of all components of the shoal ecosystems.