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Barred Sand Bass Essential Fishery Information
Essential Fishery Information (EFI) includes data on age, growth, reproduction, and other life history characteristics that are important for managing a sustainable fishery. During the 1980s, barred sand bass (Paralabrax nebulifer) became increasingly popular; up to an estimated 4.2 million barred sand bass were caught by recreational anglers in 1988. Catches remained high into the 1990s; however, fishery-dependent and fishery-independent data sources suggest significant population declines over the last decade.
Fish populations may adapt to exploitation over time by increasing recruitment and/or growth rates, or by reducing natural mortality. However, at high levels of exploitation, a population may reach a critical low, becoming less resilient and moving toward depletion.
Regulatory changes adopted in 2012 set the minimum size limit for the saltwater basses at 14 inches, and the bag limit to 5 fish in any combination of barred sand bass, kelp bass and spotted bass. These regulations went into effect on March 1, 2013 (see new size and bag limits). It will likely take several years before the effectiveness of recent management changes can be assessed; however, data collected in this project will provide managers with the knowledge necessary to detect fishery concerns earlier and prevent overfishing.
Data on several reproductive, age, and growth parameters for barred sand bass are outdated or lack adequate sample sizes, and no data exist on barred sand bass spawning periodicity (fluctuations in reproductive hormone levels). These EFI are needed to evaluate the fishery's response to recent and future regulation changes, as well as oceanographic changes. In addition, these EFI will be critical components of future stock assessments and fishery management plans, further enhancing the CDFW's ability to manage this species.
The project is currently collecting the following EFI for barred sand bass:
Understanding the reproductive potential of barred sand bass depends not only on how long fish stay at a spawning aggregation but how frequently they spawn. We can tell if a female has recently spawned by the presence of postovulatory follicles in the ovaries. When we know what proportion of females have postovulatory follicles, we can estimate spawning frequency. In a previous study, female barred sand bass were shown to spawn about every day and a half, but most samples were collected toward the tail end of peak spawning season and so frequency intervals may have been underestimated. To re-examine spawning frequency, 248 barred sand bass were collected from the Huntington Flats spawning grounds over the course of the spawning season (June through August 2011), gonads were removed and histologically sectioned and stained to visualize the internal gonadal structures and to identify postovulatory follicles.
Histological section from ovary of a barred sand bass collected at the Huntington Flats spawning aggregation.
Several stages of oocyte development are present. Postovulatory follicle is labeled.
Findings to Date
The previous spawning fraction and spawning interval estimates for barred sand bass were taken over a two week period in July. To determine if these estimates vary across the spawning season, we quantified ovarian activity using histological cross-sections from 208 barred sand bass females collected on the San Pedro Shelf from June to September 2011. We were able to classify the overall reproductive state of the ovaries and assign them reproductive phases. We found the typical monthly reproductive phases to be:
- June (developing: ovaries beginning to develop but not ready to spawn)
- July and August (spawning capable: fish are developmentally capable or actively spawning)
- September (regressing: cessation of spawning)
The spawning fraction (S) was estimated using the postovulatory follicle (POF) method to determine the proportion of mature females with POFs < 24 hours old. The spawning fraction varied by month (x2 (3, N =208) =23.1, p < 0.001) with the proportion of spawning females peaking in July and August, although no difference was noted between these two months (x2 (1, N =166) =0.836, p = 0.361).
During July and August spawning season (S =0.54, upper 95% confidence limit=0.6220 and lower 95% confidence limit=0.4722), the average spawning interval was 1.85 days, with daily spawning in 42% of fish. In contrast, POFs were less abundant in June (S = 0.17, upper 95% confidence limit=0.3467 and lower 95% confidence limit=0.0607) and September (S =0.11, upper 95% confidence limit=0.3405 and lower 95% confidence limit=0.0186), further indicating spawning season lasts from July-August.
We compared the monthly proportion of recently spawned fish, (fish that spawned within four hours of capture), and found July was significantly higher than August (x2 (1, N =166) =6.75, p = 0.009) indicating spawning peaks in July. Our results highlight the importance of sampling throughout the spawning season in order to avoid over- or underestimating the total number of spawning events per individual per year.
Female barred sand bass collected in 2011 showed evidence of peak spawning activity in July.
Spawning is triggered in many species by environmental cues. In marine environments, common cues include lunar and/or tidal flux. These cues are important for species to mate successfully and may indicate the best times for survival of fertilized eggs and larvae. Barred sand bass may experience other environmental cues such as increased day length or increased temperature that drive them to form spawning aggregations, but there may also be additional, closely related environmental cues throughout the spawning season that trigger spawning pulses. Understanding which cues trigger spawning in barred sand bass is important for understanding how and why reproductive potential sometimes varies from year to year.
Reproductive hormones fluctuate with respect to environmental cues and may peak during spawning pulses. By analyzing hormone concentrations in barred sand bass over the course of the breeding season, we may determine if there is a relationship with lunar cycles and/or tidal flux. To determine the relationship between environmental cues and spawning, blood plasma was collected from 264 barred sand bass over the course of the 2011 spawning season at the Huntington Flats spawning grounds to test for concentrations of estradiol, progesterone and 11-ketotestosterone (11-KT). Staff also seek to determine how hormone concentrations relate to fish size, gonad size and the presence/absence of post-ovulatory follicles produced by females following spawning events.
Findings To Date
We obtained blood plasma from 264 barred sand bass (160 females, 102 males, 2 unknowns) to analyze reproductive hormone levels (estradiol, 11-KT, progesterone) during spawning season. We calculated mean hourly and weekly levels of each hormone to identify any peak(s) in hormone concentration during a 24-hour period and during spawning season. We were able to collect blood plasma samples between the hours of 7:00 a.m. and 3:00 p.m. During those times, female levels of estradiol in July and August were significantly higher before noon than after noon.
Male levels of 11-KT peaked once during the week of July 20. 11-KT triggers spermatogenesis in males and so the peak in late July suggests most males have reached their peak in potential reproductive output (i.e., high GSI due to proliferation of spermatozoa) by the end of July. Relatively low levels in late June and August were similar to values obtained on a single sampling date in mid-September.
Female levels of estradiol peaked in late June, late July, and mid-August. The peaks in July and August were of similar magnitude, and by late August/early September estradiol levels had fallen again. By mid-September, estradiol levels in 9 females were near zero, indicating spawning had already ceased. Preliminary analyses suggest estradiol levels may be influenced by ocean temperature.
Female levels of progesterone were relatively stable from late June until mid-August. Peaks in progesterone occur at the end of spawning season; the highest peak in female levels of progesterone occurred in late August.
Barred sand bass are serial spawners, meaning they may spawn many times over the course of a spawning season. As in other serial spawners, barred sand bass ovaries contain eggs at several different stages of development; however, only the hydrated eggs will be spawned. Batch fecundity refers to the number of eggs released in one spawning event. By determining the batch fecundity for several individuals over a wide size range, we can develop a batch fecundity-size relationship which will allow us to estimate the batch fecundity of females measured in the field. Batch fecundity will be an important parameter for estimating reproductive potential of barred sand bass. Staff collected gonads from 248 barred sand bass at the Huntington Flats spawning grounds over the course of the 2011 spawning season. Staff will count the number of hydrated eggs in the ovaries to determine batch fecundity for individual fish.
Findings to Date
Reliable batch fecundity estimates are essential for calculating total annual fecundity; however, previous batch fecundity studies on barred sand bass contained small sample sizes. We collected barred sand bass throughout the 2011 spawning season (June-August) and into September.
Batch fecundity was calculated using the hydrated oocyte method, where the number of hydrated oocytes was counted per 0.10 g of whole-mounted ovarian tissue and multiplied by ovary mass. Active or imminent spawning females were identified by the presence of hydrated oocytes and post-ovulatory follicles (POFs) in histological cross-sections taken from the ovaries of 208 females. Ovaries were categorized by POF age (Day 0= <4 hours, Day 1 = 4-24 hours, Day 2 = >24 hours), but only females with Day 2 POFs (n = 46) were used for obtaining a batch fecundity size relationship.
Based on the preliminary model predicted from females with Day 2 POFs (n =18), hydrated oocyte counts for a subset of females with Day 0 (n = 6) and/or Day 1 (n = 13) POFs underestimated batch fecundity by an average of 26% and 20%, respectively. Batch fecundity was linearly related to ovary mass (y = 1107x + 5147.5, R2 = 0.93) and the relationship with fish standard length (mm) was best described by the power function, y = 0.0086x2.8028, R2 = 0.72. None of the females collected in September met the criteria for estimating batch fecundity.
Age Structure and Validation
Cross-section of a sagittal otolith taken from a barred sand bass collected in the 1990s. The otolith was aged to 17 years. CDFW file photo.
The age of most finfish can be determined by analysis of their otoliths. Otoliths are hard structures located in the inner ear that grow as the fish grows by adding layers of calcium carbonate. The addition of layers is affected by seasonal changes in growth rate, so that calcium carbonate rings may form annually and can be counted similar to tree rings. We collected otoliths from 352 barred sand bass at Huntington Flats in 2011. By counting the rings on the otoliths we can estimate the age structure of barred sand bass at the Huntington Flats spawning aggregation in 2011. While this is a common ageing technique in fish, no one has ever validated that the ring pattern is annual across size classes in barred sand bass. To examine this, we will keep barred sand bass of several size classes in captivity for at least one year. Shortly upon capture we will inject a chemical marker called oxytetracyline (OTC) into the musculature that will be naturally incorporated into the otoliths. After a year, we will remove the otoliths and confirm the periodicity of the ring pattern.
We are currently processing otoliths. Stay tuned!