Auke Bay Laboratory (ABL)

Marine Salmon Interactions Program

Southeast Coastal Monitoring Epipelagic Ichthyofauna Sampling in 2005

Biologists for ABL’s Southeast Coastal Monitoring (SECM) project completed four research cruises in 2005. This was the ninth year of SECM sampling for juvenile Pacific salmon (Oncorhynchus spp.), ecologically-related species, and associated biophysical data in the marine waters of southeastern Alaska. Cruises were conducted from the NOAA vessel John N. Cobb in late May, June, July, and August. In June and July, surface trawling and associated oceanographic sampling were done in both the northern and southern regions of Southeast Alaska as part of a 3-year study designed to compare the utility of using juvenile pink salmon (O. gorbuscha) abundances to forecast adult returns.

Other objectives of the SECM research are to investigate the role of juvenile salmon in the coastal marine ecosystem by identifying relationships among biophysical parameters that influence habitat use, marine growth, prey utilization, energetic condition, predation, stock interactions, and migration patterns. Monthly cruise reports and annual reports for the SECM project are available online at http://www.afsc.noaa.gov/abl/MarSalm/ablmsi.htm.

In 2005, Icy Strait and Upper Chatham Strait in northern Southeast Alaska (NSE) and Lower and Middle Clarence straits in southern Southeast Alaska (SSE) were sampled. A total of 20-23 trawl hauls were made in June and July in each region. Straits habitat in NSE was also sampled in May (biophysical oceanography only) and August (eight trawl hauls along with biophysical oceanography); coastal habitat off of Icy Point was sampled only in May (biophysical oceanography only).

In comparing the catches between the two regions of Southeast Alaska in June and July, total catches of juvenile salmon were similar: 2,941 in NSE and 3,005 in SSE (Table 1 below). The frequency of occurrence of each species was similarly high in the two regions in June, but was lower in SSE than in NSE for some species in July. Juvenile chum salmon (O. keta) were relatively more abundant in NSE, while pink salmon were relatively more abundant in SSE.

Unusually large numbers of pink salmon were captured in August in NSE, but no comparable sampling was conducted in SSE. These catches constituted the highest August catch-per-unit-effort (CPUE) for juvenile pink salmon in the 9-year history of SECM sampling; 2005 is the only year in which CPUE for pink salmon was highest in August.

A total of 645 juvenile coho were caught in the two regions, 51 (7.9%) of which were missing the adipose fin, indicating the possible presence of a coded-wire tag. Of the coho salmon with missing adipose fins, 15 had coded-wire tags from stocks originating in Southeast Alaska, as well as in Washington and Oregon. The high percentage of fish with missing adipose fins caught in SSE that did not have a coded-wire tag suggests that these fish came from releases of fin-clipped coho salmon in the Pacific Northwest for selective fisheries management. Laboratory processing of juvenile pink and chum salmon samples is ongoing to collect biological information and determine the stock composition of otolith-marked juvenile chum salmon released by enhancement facilities in both regions of Southeast Alaska.

For the second consecutive year, and the third year for the 9-year SECM data series, unusually warm temperatures were observed in Southeast Alaska; these warm years coincided with earlier migration of juvenile salmon from nearshore habitats into strait habitats and the Gulf of Alaska. For example, although peak catches of juvenile pink and chum salmon typically occur in July, catches were highest in June during the warm years of 1998, 2004, and 2005. This first year of sampling in both SSE and NSE confirmed that migration occurred earlier throughout the region.

Other observations of note included the unusual presence of market squid (Loligo opalescens) and relatively high jellyfish biomass in SSE. In June, the jellyfish Aequoria sp. and Aurelia sp. were abundant in trawls in SSE, while little jellyfish biomass was retained in trawls in NSE. In July, these species were about half as abundant in SSE, and Cyanea sp. became conspicuous in NSE. Also conspicuous in July were ichthyofauna associated with these large jellyfish: prowfish (Zaprora silenus), crested sculpin (Blepsias bilobus), and young-of-the-year pollock (Theragra chalcogramma).

By Molly Sturdevant and Joe Orsi


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AFSC Quarterly
Research Reports July-Sept 2005