Status of Stocks & Multispecies Assessment Program
A FRESH Look at Fish Reproductive Biology and its Effect on Fisheries Assessment and Management
Paul Spencer gave a presentation titled "Incorporating reproductive biology into stock assessments: experiences from Alaska and the U.S. West Coast" at the Fish Reproduction and Fisheries Conference (FRESH) in Vigo, Spain, on 20 May.
The FRESH project was funded from 2007 to 2011 and consists of a network of scientists interested in the biological processes of fish reproduction and the incorporation of reproductive biology into fisheries assessment and management. The FRESH project has produced several workshops and peer-reviewed publications, with the Vigo conference being the final official activity.
The conference consisted of over 50 presentations organized into the following six sessions: 1) Evaluate inputs used to estimate reproductive potential; 2) Standardized methods to estimate total egg production; 3) Causes of variation in reproductive parameters; 4) Methods of examining the causes of variation; 5) The impact of changes in stock reproductive potential on scientific advice; and 6) Methods to include stock reproductive potential in stock assessments.
Spencer delivered the keynote presentation for Session 6, which reviewed current research on reproductive biology being conducted in Alaska and the U.S. West Coast. The Bering Sea/Aleutian Islands Pacific ocean perch and the Gulf of Alaska walleye pollock assessments were used to evaluate how reproductive processes such as maternal effects in egg and larval survival and weight-specific fecundity may affect the estimation of relative stock size, stock-recruitment parameters, and fishing rate reference points.
A particularly interesting finding is that the fishing mortality associated with maximum sustainable yield (Fmsy) increases as the egg production per spawner weight increases. This could affect the estimation of Fmsy for stocks in which egg production is erroneously assumed to be linear to spawning stock biomass (a common assumption in stock assessments). The proceedings of the FRESH conference will be published in the journal Fisheries Research.
By Paul Spencer
Chum Salmon Bycatch Analysis
Scientists from the AFSC continued to contribute to the analysis of groundfish fisheries in order to reduce chum salmon bycatch. The purpose of these analyses are to evaluate the trade-offs of the different alternative management approaches (and numerous sub-options) being considered by the North Pacific Fishery Management Council. The proposed management measures include hard caps (fixed bycatch limits); bycatch limits that trigger time and area closures; and a fleet-managed program for 4–7 day real-time bycatch area closures on (so-called rolling hotspot (RHS) program).
Part of the AFSC's contribution involved integrating information collected by fisheries observers on the numbers and lengths of chum salmon taken incidentally during groundfish fishing operations with the genetic analyses on the stock composition compiled by the Auke Bay Laboratories (ABL). Of particular note was the development which corrects stock composition estimates relative to the size (and hence age) of chum salmon taken incidentally in the pollock fishery.
For example, if 100 fish projected from last year’s bycatch would have returned to a river (or hatchery) this year, then last year's genetic estimates of the bycatch would apply (not this year's). This allows improved estimates on the impacts the bycatch totals have on specific regions where chum salmon return (e.g., providing answers to questions such as "How many more chum salmon would have returned to western Alaska had no bycatch occurred?").
Results confirmed early studies that indicated that during the early part of the summer fishery (June–July) a higher fraction of the chum salmon bycatch originates from western Alaska (about 24%) compared to later in the year (August–October) when the proportion decreases to about 14%. These results also indicate that more than half of the chum salmon bycatch originates from rivers and hatcheries in Japan and Russia. The estimated ratio of western Alaska bycatch relative to the number of regional returning chum salmon averaged less than 1% (with the highest year estimated to have had a 1.5% reduction in returning salmon due to bycatch in the pollock fishery).
Other types of analyses that were included in the draft Environmental Assessment submitted to the Council included two novel approaches to evaluating status quo management measures. In particular, aspects of the RHS program were evaluated by examining detailed vessel-specific patterns in bycatch in recent years. A second approach was to impose a pseudo RHS program on the historical data (prior to the existence of such programs) and estimating the numbers of salmon that would have been avoided in the bycatch had such a program been in place.
At its June meeting held in Nome, Alaska, the Council revised and restructured the suite of alternatives and options and requested new information. The Council will thus review the analysis two more times prior to making a final decision in mid-2012.
