California Sea Grant College Program
Assessing changes in life history traits and reproductive function of CA sheephead across its range: historical comparisons and the effects of fishing
- Author(s): Caselle, Jennifer E.
- Lowe, Christopher
- et al.
Project Hypotheses The specific predictions can be summarized as: P1: Life history parameters will vary across the range of this species and spatial differences in life histories will be determined by population density, sex ratios, environmental factors, and fishing pressure. P2: Fish collected in this study will be smaller and younger than fish collected from previous times (historical collections from 1970-1980) and the effects will be greatest at sites where fishing is intense (i.e. southern California vs. Baja California). P3: Fish collected in this study will change sex from female to male at a younger age and smaller size than previous times, especially at sites where fishing is intense (as predicted by size advantage model). P4: As a result of P3 (females mature younger and smaller), operational sex ratios will increase (also predicted by size advantage model). P5: Stricter harvest limits may have initiated recovery in heavily exploited populations and may result in increases in lengths, the timing of maturation, and the timing of sex change. P6: Individual growth rates will differ both spatially (sites across the species range) and temporally (historical vs. 1998 vs. this study) and variance will be more related to site location (e.g. water temperature and food availability) than type or amount of fishing. P7: Ultrasound techniques will provide a cost effective, non-destructive, and reliable tool to assess sex, fecundity, and reproductive state in these important fish. P8: Radioimmunoassays of estradiol and testosterone will verify the utility of visual assessments of sexual state and provide a non-destructive means to survey reproductive function during the breeding season. P9: Potential reproductive output will be less in this study than that of past studies at sites where fishing pressure is intense.