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.

Fish consumption by harbor seals (Phoca vitulina) in the San Juan Islands, Washington

The harbor seal (Phoca vitulina) is a large-bodied and abundant predator in the Salish Sea ecosystem, and its population has recovered since the 1970s after passage of the Marine Mammal Protection Act and the cessation of bounties. Little is known about how this large predator population may affect the recovery of fish stocks in the Salish Sea, where candidate marine protected areas are being proposed. We used a bioenergetics model to calculate baseline consumption rates in the San Juan Islands, Washington. Salmonids (Oncorhynchus spp.) and herring (Clupeidae) were the 2 most energetically important prey groups for biomass consumed by harbor seals. Estimated consumption of salmonids was 783 (±380 standard deviation [SD]) metric tons (t) in the breeding season and 675 (±388 SD t in the nonbreeding season. Estimated consumption of herring was 646 (±303 SD) t in the breeding season and 2151 (±706 SD) t in the nonbreeding season. Rockfish, a depressed fish stock currently in need of population recovery, composed one of the minor prey groups consumed by harbor seals (84 [±26 SD] t in the nonbreeding season). The variables of seal body mass and proportion of prey in seal diet explained >80% of the total variation in model outputs. Prey groups, such as rockfish, that are targeted for recovery may still be affected by even low levels of predation. This study highlights the importance of salmonids and herring for the seal population and provides a framework for refining consumption estimates and their confidence intervals with future data.

Distribution and abundance of Dungeness crab and crangon shrimp, and dredging-related mortality of invertebrates and fish in Grays Harbor, Washington

The impacts of widening and deepening the existing navigation channel in Grays Harbor on Dungeness crab, crangon shrimp and fish was investigated. The spatial and temporal distribution of these organisms was studied using an otter trawl and ring nets, and the uptake of organisms by dredges was estimated from samples collected on working hopper and pipeline dredges. ... Impacts of the dredging project on crabs, shrimp and fish could be associated with entrainment, food loss and toxicants released from sediments. Scenarios are presented that predict impacts. Suggestions for reducing impacts are given.

Examination of the foraging habits of Pacific harbor seal (Phoca vitulina richardsi) to describe their use of the Umpqua River, Oregon, and their predation on salmonids

The increase in harbor seal (Phoca vitulina richardsi) abundance, concurrent with the decrease in salmonid (Oncorhynchus spp.) and other fish stocks, raises concerns about the potential negative impact of seals on fish populations. Although harbor seals are found in rivers and estuaries, their presence is not necessarily indicative of exclusive or predominant feeding in these systems. We examined the diet of harbor seals in the Umpqua River, Oregon, during 1997 and 1998 to indirectly assess whether or not they were feeding in the river. Fish otoliths and other skeletal structures were recovered from 651 scats and used to identify seal prey. The use of all diagnostic prey structures, rather than just otoliths, increased our estimates of the number of taxa, the minimum number of individuals and percent frequency of occurrence (%FO) of prey consumed. The %FO indicated that the most common prey were pleuronectids, Pacific hake (Merluccius productus), Pacific stag-horn sculpin (Leptocottus armatus), osmerids, and shiner surfperch (Cymatogaster aggregata). The majority (76%) of prey were fish that inhabit marine waters exclusively and fish found in marine and estuarine areas (e.g. anadromous spp.) which would indicate that seals forage predominantly at sea and use the estuary for resting and opportunistic feeding. Salmonid remains were encountered in 39 samples (6%); two samples contained identifiable otoliths, which were determined to be from chi-nook salmon (O. tshawytscha). Because of the complex salmonid composition in the Umpqua River, we used molecular genetic techniques on salmonid bones retrieved from scat to discern species that were rare from those that were abundant. Of the 37 scats with salmonid bones but no otoliths, bones were identified genetically as chinook or coho (O. kisutch) salmon, or steelhead trout (O. mykiss) in 90% of the samples.

Molecular methods for the genetic identification of salmonid prey from Pacific harbor seal (Phoca vitulina richardsi) scat

Twenty-six stocks of Pacific salmon and trout (Oncorhynchus spp.), representing evolutionary significant units (ESU), are listed as threatened or endangered under the Endangered Species Act (ESA) and six more stocks are currently being evaluated for listing. The ecological and economic consequences of these listings are large; therefore considerable effort has been made to understand and respond to these declining populations. Until recently, Pacific harbor seals (Phoca vitulina richardsi) on the west coast increased an average of 5% to 7% per year as a result of the Marine Mammal Protection Act of 1972 (Brown and Kohlman2). Pacific salmon are seasonally important prey for harbor seals (Roffe and Mate, 1984; Olesiuk, 1993); therefore quantifying and understanding the interaction between these two protected species is important for Morphobiologically sound management strategies. Because some Pacific salmonid species in a given area may be threatened or endangered, while others are relatively abundant, it is important to distinguish the species of salmonid upon which the harbor seals are preying. This study takes the first step in understanding these interactions by using molecular genetic tools for species-level identification of salmonid skeletal remains recovered from Pacific harbor seal scats.

Local distribution and abundance of swimming crabs (Callinectes spp. and Arenaeus cribrarius) on a tropical arid beach

Distribution, abundance, and several population features were studied in Ensenada de La Vela (Venezuela) between 1993 and 1998 as a first step in the assessment of local fisheries of swimming crabs. Arenaeus cribrarius was the most abundant species at the marine foreshore. Callinectes danae prevailed at the estuarine location. Callinectes bocourti was the most abundant species at the offshore. Abundances of A. cribrarius and C. danae fluctuated widely and randomly. Ovigerous females were almost absent. Adults of several species were smaller than previously reported. This study suggests that fisheries based on these swimming crabs probably will be restricted to an artisanal level because abundances appear too low to support industrial exploitation.

Bycatch and catch-release mortality of small sharks in the Gulf coast nursery grounds of Tampa Bay and Charlotte Harbor

The bays and estuaries of the southeast United States coast generally are thought to serve as nursery areas for various species of coastal sharks, where juvenile sharks find abundant food and are less exposed to predation by larger sharks. Because these areas typically support substantial commercial and recreational fisheries, fishing mortality of sharks in the nurseries particularly by bycatch, may be significant. This two-year project assessed the relative importance of two estuaries of the southwest Florida Gulf coast, Tampa Bay and Charlotte Harbor/Pine Island Sound, as shark nursery areas, and examined potential fishing mortality of these young sharks in the nurseries.

Textural and compositional variations in beach sands along Karachi coast

The texture of clastic sediments is a fairly reliable index of the erosional history and energy conditions of the depositional environment, while its mineralogy reflects the composition of the source rocks. The beach sands of Clifton, Sandspit, Hawkesbay and Paradise Point were studied to determine their erosional history, depositional environment and their source

The bacterial flora and their possible association with spoilage in a variety of fresh-water fish: Cyprinus carpio. var. communis

The bacteria from a variety of fresh-water fish, Cyprinus carpio. var. communis, showed the presence of micrococci, Gram positive and Gram negative rods. These have been characterized as far as was possible. Of thirty-eight strains of bacteria used, only six strains were considered as causing spoilage of fish flesh in experiments where flesh was incubated with individual cultures of the bacteria. These six strains had been found on the surface and/or intestine of the fish and support the suggestions that, after death, invasion of flesh by bacteria from the surface and intestine could be the cause of bacterial spoilage of fish.

Fishes of Ceylon: a catalogue, key and bibliography

A knowledge of the specific composition of Ceylon fish fauna is essential to any programme of development of commercial fisheries, or the study of Ceylon's ichthyology and the need for cataloguing it has been keenly felt for many years. The need for cataloguing the whole of Ceylon's flora and fauna was stressed by the Natural Science Section of the Ceylon Association for the Advancement of Science during its 1952 annual sessions and it was then that the writer agreed to help satisfy this need by compiling an up-to-date check list of species of two families of fishes, the Clupeidae and the Carangidae, which are important in the beach seine fishery which he was studying at that time. In the course of this work it was decided to expand the check-list to make it comprehensive of all species of fish that have been recorded from Ceylon to date and to supply keys for their identification. This has involved a screening of the pioneer works of Bennet (1834) and Day (1878-1889) and the many subsequent references to Ceylon fish scattered through various scientific journals and other publications, some of them long out and now almost unobtainable.