Research Document - 2007/086

Potential impacts of the British Columbia herring roe fishery on the spatial and temporal distribution of herring spawn: examination of the serial depletion hypothesis

By Hay, D.E., P.B. McCarter and K.S. Daniel

Abstract

The British Columbia herring roe fishery is conducted on or near inter- and sub-tidal spawning locations. It is a conservative fishery, taking a maximum of 20 percent of the spawning biomass in any of the five major assessment areas. The assessment areas are large and may contain a number of different spawning and fishing sites. As a rough approximation, each assessment area consists of about 5-10 smaller geographic units, called sections. Sections are geographic units used almost exclusively by the Fisheries and Oceans Canada Science Branch. In most years the fishery may be concentrated in a few sections, so the section-specific catch rates sometimes exceed twenty percent. Some observers suggest that these localized intense fisheries may lead to serial depletion of unique spawning components of the populations. This report addresses the hypothesis that, since its inception in the early 1970’s, the herring roe fishery has led to systematic reduction in the number of distinct spawning locations. We examined the spatial-temporal patterns of spawning by comparing the frequency of section-specific spawning between two periods: a 31-year period between 1940 and 1970 (prior to the roe fishery, when catch rates were very high in most years) and a 36 year period corresponding to the roe fishery, from its initiation to the present. When examined among assessment areas, there was no evidence of a decrease in the frequency of spawning between the two periods. We also compared the temporal pattern of catch and spawn data for each of the approximately 100 geographic sections. Using the annual assessment estimates (from 2006) we scaled spawn data units to metric tonnes and then examined the temporal history of spawn and catch in each section. We found three instances where a cessation of spawning coincided approximately with a roe fishery. In each instance, however, more detailed analyses showed that none represented a clear example of depletion following a fishery. Instead these examples represented fisheries that occurred in locations where spawning activity was not consistent in time or space in years prior to the fishery, or where the geographic dimensions of the section were exceptionally small. The geographic range of each section is arbitrary, and not based on biology. We show that in one case, in the central coast of BC, the simplest explanation is a slight shift in spawning between adjacent spawning sites in sections that are much smaller than others on the BC coast. Herring spawn locations are dynamic and changes in spawning patterns are evident from the results of this report and many previous studies. However our results indicate that there is no evidence to support the hypothesis of serial depletion during the roe fishery as an explanation for those changes. The report concludes with a discussion of the tradeoffs and associated risks between the managerial and logistical benefits and of taking the (total allowable catch) TAC in a fewer number of larger openings in small areas (few sections) versus the preferable biological goal of spreading the TAC and fishing effort to a larger number of smaller openings over a broad geographic area (many sections). This report contains two substantial appendices. One is an annotated list of each herring section, showing graphical analyses and key statistics on spawning and catch data from 1940-2006 (mean spawning date, cumulative spawn area and cumulative catches by season).

The second appendix is a brief report, titled “Spatial and temporal distribution of the fishery” that describes the development of a spatial data base of the herring roe and discusses the technical limitations to geo-referencing herring roe catch data.

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