Description of Index An objective of the Alaska Fisheries Science Center (AFSC), Auke Bay Laboratories (ABL) Southeast Alaska Coastal Monitoring (SECM) project is to understand the effects of climate and ocean on year class strength of salmon and ecologically-related species in Southeast Alaska (SEAK). Since 1997, the SECM project has collected a time series of data using surface trawls and oceanographic instruments in coastal SEAK which has allowed an annual index of ecosystem metrics to be constructed and used for pre-season pink salmon (Oncorhynchus gorbuscha) forecast models. Pink salmon are an ecologically and economically important species in SEAK ($92.5 M in 2011) that do not lend themselves to traditional sibling or stock assessment models because of their brief ocean life history. However, adult returns are notoriously difficult to forecast because their brief 2-year life history includes only one ocean winter and therefore precludes the use of younger returning ocean age classes to predict cohort abundance. Thus, an SECM pink salmon pre-season forecast model was developed beginning in 2004 to 1) help fishery managers maintain sustainable fisheries, 2) meet the pre-season planning needs of the resource stakeholders in the commercial fishing industry, and 3) gain a better understand of mechanisms related to salmon production in the Gulf of Alaska (GOA) large marine ecosystem.
Status and Trends
Since 1960 pink salmon year-class success has varied widely, with harvests ranging from 3 to 78 million fish annually in SEAK. This variability may result from dynamic ocean conditions or ecological interactions that affect juvenile salmon. Additionally, pink salmon production in SEAK is predominately derived from mostly (>95%) wild stocks of varied run timings that originate from more than 2,000 anadromous streams throughout the region. Therefore, the SECM approach has been to sample 4-65 km offshore along coastal localities in the vicinity of Icy Strait on monthly research surveys. This sampling locality integrates an amalgam of SEAK stocks since it is the principal northward migration corridor in SEAK. Oceanographic sampling is conducted in May, June, July, and August, while surface trawling for epipelagic fish species is conducted in the latter 3 months as juvenile salmon are actively migrating. The SECM data has also been used to describe epipelagic fish assemblages in the Alaska Coastal Current compared to the California Current, to define Essential Fish Habitat for Pacific salmon in the U.S. Exclusive Economic Zone of Alaska, and to document life history patterns of threatened and endangered salmon stocks off SEAK. For the pink salmon forecasting, SECM data is used with other regional and basin-scale data sources to construct an ecosystem matrix of input and response variables.
Figure 1. Previous SECM pink salmon forecast model predictions (with 80% confidence intervals) and actual SEAK harvests.
Researchers from the SECM project have provided forecasting information to stakeholders of the pink salmon resource of SEAK since 2004. These forecasts have allowed stakeholders to anticipate the harvest with more certainty than previous forecasting methods. For example, in 8 of the past 9 years, SECM forecast estimates have only deviated from the actual harvests by an average of 7% ) (Fig. 1). Catch per unit effort (CPUE) data from juvenile pink salmon catches are also shared with the Alaska Department of Fish and Game (ADF&G) to help refine their SEAK pink salmon harvest forecast that is developed by a different method.
Factors Causing Observed Trends
Selected ecosystem metrics associated with SEAK adult pink harvest over the 16-year SECM time series are shown in Figure 2 below. The ranges of values below each metric are color-coded, with the highest values in green, intermediate values in yellow, and the lowest values in red. Metrics to the right of the response variable column for SEAK pink harvest are ordered by declining correlation and significance (increasing “P-value” = declining significance); the corresponding correlation coefficient “r” and “P-value” are shown below each metric. Note that in addition to CPUE, four other variables are significantly correlated with harvest (Peak migration month, North Pacific Index (NPI), %pink in June-July trawl hauls, and the ADF&G Escapement Index) and suggest an intermediate pink harvest in 2013. Additionally, this matrix shows that anomalously low (red: 2000, 2006, 2008, 2012) or high (green: 1999, 2001, 2005, 2011) return years always flag 3-5 ecosystem indicators of the respective color signal in each row. For the 2013 forecast, however, no “red” ecosystem indicators were flagged. The Icy Strait temperature index (ISTI) shown in the last column is not significantly correlated with harvest, but is an important secondary parameter to explain the error in the CPUE and harvest regression model. Mmore details about the SECM pink salmon forecasts are available on the SECM pink salmon forecast web page.