Findings of the 2016-17 Southern Salish Sea Acoustic Mid-Water Trawl Survey: Final Report to the Washington State Legislature (Funded via Senate Bill No. 5166)

The mission of the Washington Department of Fish and Wildlife (WDFW) is to preserve, protect, and perpetuate fauna and flora occurring within the territorial boundaries of Washington State. Periodic assessments of the distribution and abundance of these species is fundamental to accomplishing this mission. When funding allows, and the need warrants it, these periodic evaluations develop into long-term monitoring programs that support adaptive and proactive monitoring and management strategies.

In the inland marine waters of Washington, referred to here as the southern Salish Sea, long-term monitoring programs of various spatiotemporal scales exist for: benthic fishes occurring on deep, relatively flat, muddy bottoms (via benthic trawl); benthic fishes occurring on deep (via remotely operated vehicles) and shallow (via scuba diving), high relief, rocky bottoms; and benthic to semi-pelagic fishes occurring in the nearshore (via beach seine and lampara net). Offshore pelagic fishes, however, have not been directly sampled in any systematic way since acoustic/trawl surveys focused on pre-spawning Pacific Herring were discontinued in 2009. During the three plus decades that these acoustic/trawl surveys occurred their geographic scope was limited and their catch, by design, consisted almost entirely of herring and, secondarily, Northern Anchovy.

Recognizing the substantial knowledge gap surrounding use of the pelagic environment by diverse fish species, and leveraging increased interest in management of marine resources, in 2015 the WDFW advocated for a systematic assessment of offshore waters of the southern Salish Sea. Through collaboration with members of the Senate, most notably Senator Christine Rolfes, Substitute Senate Bill 5166 was signed into law on May 7th, 2015. The bill directed the WDFW to “conduct a mid-water trawl survey at various depths throughout Puget Sound to evaluate the prevalence of adults of all species of forage [and pelagic] fish,” and to use the information obtained to improve conservation practices.

Between February 2016 and February 2017, the WDFW surveyed 18 index reaches throughout the southern Salish Sea (i.e., greater Puget Sound) using hydroacoustics and a mid-water trawl. Sampling occurred every other month, providing seven independent evaluations of fish presence and species composition, and vertical plankton tows were paired with each station to evaluate makeup of the prey base. Though over one hundred species of fishes and invertebrates were encountered, Pacific Herring dominated the acoustic signature and the catch across most sampling reaches and time periods, with Pacific Hake prevalent in the Whidbey Basin and Hood Canal, and Northern Anchovy prevalent south of the Tacoma Narrows. Seasonal shifts in distribution were apparent for some species, however, as demonstrated by the lack of herring in sampled waters during the late winter and early spring when individuals were spawning in the nearshore. Jellyfishes were common in several regions and tended to become more so during the late spring and through the summer.

The information gained from this survey will guide forage fish conservation and fishery practices and inform resource management policy moving forward. It will also be used as a baseline against which to compare future surveys as broad-based ecosystem level management of the marine environment continue to develop. A companion report focused on biological attributes of trawl-caught fishes is currently in development.