Pacific Hake - Growth and natal origin of Pacific hake from the Georgia Basin DPS

Pacific hake (Merluccius productus) is an abundant species residing along the Pacific coast from the Gulf of California to the Strait of Georgia. It is the most common groundfish in the California Current ecosystem (Helser et al. 2008).  In Puget Sound, however, Pacific hake populations have declined dramatically in the past three decades (Figure 1), leading to a closure of the fishery in 1990 (Gustafson et al. 2000) and a designation by NOAA Fisheries as a Species of Concern in 1999.  Because Pacific hake feed on a variety of fishes and invertebrates, and are an important prey item (for sea lions, small cetaceans, and dogfish sharks), the decline of this mid-trophic level component has important ramifications for the functioning of the Puget Sound ecosystem.    
Puget Sound Pacific hake are classified as part of the Georgia Basin Distinct Population Segment (DPS), which is discrete from the highly migratory coastal DPS (Figure 2a).  The Biological Review Team (BRT) that reviewed the status of the Georgia Basin DPS noted that in addition to the decline in Puget Sound hake abundance, another cause for concern was a marked decrease in mean hake size and age at maturity (Gustafson et al. 2000).  In contrast, these patterns were not observed as strongly in the Strait of Georgia populations (King and McFarlane 2006), which are also part of the Georgia Basin DPS.  The BRT were also concerned by uncertainties in the extent of mixing among stocks of the Georgia Basin DPS (Gustafson et al. 2000). This issue is important because if mixing is limited, then the problems faced by the Puget Sound stock are more important for its potential recovery.
Puget Sound hake spawn in large aggregations in a few distinct locations, which are associated with sources of freshwater.  Unfortunately these sites occur in somewhat degraded areas, particularly with regard to oxygen concentration.  Therefore we hypothesize that the hypoxic and otherwise degraded conditions of these spawning areas have led to depressed juvenile growth, which in turn can have detrimental consequences for the population.  Woodbury et al. (1995) found that juvenile growth of the coastal stock varied from year to year and was likely related to environmental conditions.  They also speculated that year-class strength might be related to early juvenile growth.  
Another goal of the proposed research is to produce an indicator for the Puget Sound marine ecosystem in order to aid in the ongoing development of an Integrated Ecosystem Assessment (IEA) for Puget Sound, which is a high priority for NOAA.  Ecosystem indicators should be grounded in the ecology of the system, and juvenile hake growth suits this perfectly because it is not only a reflection of the state of the ecosystem, but is also reflects the viability of an integral component of the ecosystem.
This proposal represents a continuation of a project we initiated last year.  In our first year of research, funded by a Species of Concern grant, we obtained the following findings:
1) Otoliths sampled from recent years at the Port Susan spawning site demonstrated much reduced growth rates in the first and second years compared to otoliths sampled there 3 decades ago (Figure 3).
2) The chemical signatures of otolith edges (corresponding to the time when fish were sampled) of fish sampled from the Port Susan spawning site demonstrated strong consistency from year to year.  This will enhance our ability to associate adults with their natal origin.
3) The chemical signatures of otolith cores (corresponding to natal areas) demonstrated the potential existence of at least 3 separate sources for adults sampled at the Port Susan site (Fig. 5).
Here we propose to continue this research.  In particular, due to staffing issues at DFO, we were not able to obtain archived otolith samples from the Strait of Georgia, which represent an important contrast for the Puget Sound population.  We anticipate receiving these otoliths shortly, and.

Tags: bc, doc/noaa/nmfs/nwfsc, fe (fish ecology) division, georgia strait, growth, instrument not applicable, movement, national marine fisheries service, noaa. u.s. department of commerce, northwest fisheries science center, otolith, port susan, wa
Organization: National Oceanic and Atmospheric Administration, Department of Commerce