New insights into the diets of harbor seals (Phoca vitulina) in the Salish Sea revealed by analysis of fatty acid signatures

Harbor seals (Phoca fvitulina) are an abundant predator along the west coast of North America, and there is considerable interest in their diet composition, especially in regard to predation on valued fish stocks. Available informationon harbor seal diets, primarily derived from scat analysis, suggests that adult salmon (Oncorhynchus spp.), Pacific Herring (Clupea pallasii), and gadids predominate. Because diet assessments based on scat analysis may be biased, we investigated diet composition through quantitative analysis of fatty acid signatures. Blubber samples from 49 harbor seals captured in western North America from haul-outs within the area of the San Juan Islands and southern Strait of Georgia in the Salish Sea were analyzed for fatty acid composition, along with 269 fish and squid specimens representing 27 potential prey classes. Diet estimates varied spatially, demographically, and among individual harbor seals. Findings confirmed the prevalence of previously identified prey species in harbor seal diets, but other species also contributed significantly. In particular, Black (Sebastes melanops) and Yellowtail (S. flavidus) Rockfish were estimated to compose up to 50% of some individual seal diets. Specialization and high predation rates on Black and Yellowtail Rockfish by a subset of harbor seals may play a role in the population dynamics of these regional rockfish stocks that is greater than previously realized.

Fatty acid composition of red drum maintained by fishmeal, fish oil substitutes in diets

Recent research by the authors evaluated strategies to reduce fishmeal and fish oil in diets for red drum by substituting terrestrial proteins and lipids while maintaining beneficial fatty acids with DHA supplements derived from marine algae. Results suggested fatty acid-enriched finishing diets can be used with growout diets containing little or no fishmeal and fish oil to achieve the desired DHA content in the final fish fillets.

In utero domoic acid toxicity: a fetal basis to adult disease in the California sea lion (Zalophus californianus)

California sea lions have been a repeated subject of investigation for early life toxicity, which has been documented to occur with increasing frequency from late February through mid-May in association with organochlorine (PCB and DDT) poisoning and infectious disease in the 1970's and domoic acid poisoning in the last decade. The mass early life mortality events result from the concentrated breeding grounds and synchronization of reproduction over a 28 day post partum estrus cycle and 11 month in utero phase. This physiological synchronization is triggered by a decreasing photoperiod of 11.48 h/day that occurs approximately 90 days after conception at the major California breeding grounds. The photoperiod trigger activates implantation of embryos to proceed with development for the next 242 days until birth. Embryonic diapause is a selectable trait thought to optimize timing for food utilization and male migratory patterns; yet from the toxicological perspective presented here also serves to synchronize developmental toxicity of pulsed environmental events such as domoic acid poisoning. Research studies in laboratory animals have defined age-dependent neurotoxic effects during development and windows of susceptibility to domoic acid exposure. This review will evaluate experimental domoic acid neurotoxicity in developing rodents and, aided by comparative allometric projections, will analyze potential prenatal toxicity and exposure susceptibility in the California sea lion. This analysis should provide a useful tool to forecast fetal toxicity and understand the impact of fetal toxicity on adult disease of the California sea lion.

Domoic acid contamination within eight representative species from the benthic food web of Monterey Bay, California, USA

Benthic food webs often derive a significant fraction of their nutrient inputs from phytoplankton in the overlying waters. If the phytoplankton include harmful algal species like Pseudo-nitzschia australis, a diatom capable of producing the neurotoxin domoic acid (DA), the benthic food web can become a depository for phycotoxins. We tested the general hypothesis that DA contaminates benthic organisms during local blooms of P. australis, a widespread toxin producer along the US west coast. To test for trophic transfer and uptake of DA into the benthic food web, we sampled 8 benthic species comprising 4 feeding groups: filter feeders (Emerita analoga and Urechis caupo); a predator (Citharichthys sordidus); scavengers (Nassarius fossatus and Pagurus samuelis) and deposit feeders (Neotrypaea californiensis, Dendraster excentricus and Olivella biplicata). Sampling occurred before, during and after blooms of P. australis in Monterey Bay, CA, USA during 2000 and 2001. DA was detected in all 8 species, with contamination persisting over variable time scales. Maximum DA levels in N. fossatus (674 ppm), E. analoga (278 ppm), C. sordidus (515 ppm), N. californiensis (145 ppm), P. samuelis (56 ppm), D. excentricus (15 ppm) and O. biplicata (3 ppm) coincided with P. australis blooms, while DA levels in U. caupo remained above 200 ppm (max. = 751 ppm) throughout the study period. DA in 6 species exceeded levels thought to be safe for higher level consumers (i.e. ≥20 ppm) and thus is likely to have deleterious effects on marine birds, sea lions and the endangered California sea otter, known to prey upon these benthic species.