2002-2007 WDFW Scientific Bottom Trawl Surveys in the Southern Salish Sea: Species Distributions, Abundance, and Population Trends

The Washington Department of Fish and Wildlife (WDFW) is charged with managing the fauna of the state of Washington on behalf of its residents. At its core, this management consists of determining when and where organisms are found, assessing their abundance, monitoring changes in distribution and abundance over time, and developing policies that ensure continued persistence of populations and the habitats upon which they rely. In order to adequately document and understand the distribution and abundance of marine bottomfish in the southern Salish Sea (defined as the U.S. portions of the Straits of Georgia and Juan de Fuca, the San Juan Archipelago, and Puget Sound), the Washington Department of Fisheries (WDF) (which later became part of the WDFW) began conducting systematic scientific bottom trawling in 1987.

This report contains detailed results for the WDFW’s scientific bottom trawl surveys conducted from 2002 through 2007, inclusive. A total of 747 tows were completed during the months of April-June from 2002 to 2007 throughout the southern Salish Sea (“Puget Sound”), covering a total area of 613 ha in four depth strata (5-20 fa, 21-40 fa, 41-60, >60 fa). Each of the nine regions of Puget Sound was surveyed at least twice with a two- or three-year gap between sampling periods, and the Eastern and Western Straits of Juan de Fuca were surveyed three times. In an effort to obtain a holistic view of the biological composition of the bentho-demersal community, all species collected with the trawl – including invertebrates and non-bottomfish – were identified to the lowest possible taxonomic level, counted, and weighed. Population abundance and biomass estimates were then extrapolated from species counts and weights for each depth stratum and region.

Results of these estimates are first examined for each of the nine regions (South Sound, Central Sound, Hood Canal, Whidbey Island, Discovery Bay, Eastern and Western Straits of Juan de Fuca, San Juan Islands, and Georgia Basin), followed by a Sound-wide summary, and then examined by species group with more detailed analyses for a select few species. Individual species examined in more detail include Spotted Ratfish, English Sole, Starry Flounder, Pacific Sanddab, Rock Sole, North Pacific Spiny Dogfish, Walleye Pollock, Pacific Hake, and Pacific Cod; analyses for each consist of Sound-wide densities, depth distributions, length-frequencies, and hot spot maps.

Overall, Central Sound supported the highest fish biomass while Whidbey Island supported the highest average fish abundance. Spotted Ratfish and English Sole were the most dominant single species in terms of both biomass and abundance found throughout the survey. Species compositions, however, varied substantially among regions and corresponded with both depth availability and distance to ocean input. Whidbey Island and Hood Canal had the most similar assemblages, but those from most other regions deviated substantially from each other. These results should be taken into account when designing future surveys, as a Sound-wide approach might be best to capture the status of fish populations in each region within the same year.

Though not every aspect of the data are examined in this report, complete data for all species and catches are provided as an appendix, and a digital copy of the data can be obtained by contacting the WDFW Puget Sound Marine Fish Science Unit.