Research Document - 2011/058
Framework for Assessing Lobster off the Coast of Eastern Cape Breton and the Eastern and South Shores of Nova Scotia (LFAs 27-33)
By J. Tremblay, D. Pezzack, C. Denton, A. Reeves, S. Smith, A. Silva, and J. Allard
Abstract
The elements of an assessment framework are presented for Lobster Fishing Areas 27-33. These LFAs cover the Atlantic coast of Nova Scotia from Cape Breton in the northeast (LFA 27) to the south shore of Nova Scotia (LFA 33) in the southwest. There are 1639 licenses of all types in LFAs 27-33. LFAs 27-32 are spring fisheries while LFA 33 is open from late November until the end of May. The biology of lobsters in these areas is reviewed. A cluster analysis of Statistical District (SD) landings from 1947-2009 is used to delineate assessment units. Three areas with landings that trended similarly were: (i) Northeastern Cape Breton (LFA 27), (ii) Southeastern CapeBreton, ChedabuctoBay and the eastern shore (LFAs 29-32) and (iii) the South<Shore (LFA 33).
Data inputs are described. They are primarily fishery-dependent and consist of landings and effort data from the fishery, port and at-sea samples of the commercial catch and data from standard traps maintained by Fishermen and Scientist Research Society (FSRS) study participants. Landing levels are a function of abundance and a wide range of other factors but are still thought to be indicative of general trends and patterns of abundance. Catch rates (CPUE) are also affected by factors other than abundance. Commercial CPUE for LFAs 27-33 comes from two sources: mandatory logs and voluntary logs. Return rates for mandatory logs have been in the 90-100% range in recent years, with useable data in the 85-100% range. The value of mandatory log data will increase with each additional year. Voluntary logs cover a longer period than the mandatory logs but the number of logs kept is small and decreasing is some assessment units. A comparison of data in LFAs 27 and 33 indicates the means from the voluntary logs are similar to the mandatory logs.
The CPUE from FSRS traps has the advantage that it originates from standard traps set over the whole Atlantic coast of Nova Scotia. A statistical model of CPUE from the FSRS trap data in LFA 27 provides an example of what could be applied in the other assessment units (LFAs 29-32 and LFA 33).The CPUE of lobsters was used to develop indicators of abundance for sublegal and legal size lobsters. The CPUE was modeled with a mixed effects model.
Two approaches for developing indicators of reproduction are illustrated. The first is from the CPUE of ovigerous females and an example using data from the port of Little River in LFA 27, is shown. The second approach is to develop an egg index by expanding the size composition from at-sea samples to the fishery from an abundance index and using the length-fecundity relationship to estimate the total number of eggs. The egg index is developed for LFA 31a and like landings, was substantially higher in more recent years compared to 2002-2003.
Indicators of fishing pressure based on lobster size structure have low value where recruitment has fluctuated as in several of the assessment units in LFAs 27-33. The Continuous Change in Ratio (CCIR) method for estimating exploitation was applied to a number of assessment subunits. This method is based on the ratio of the number of lobsters in the harvested (legal, “exploited”) size classes to the number of lobsters in the unharvested (sublegal, “reference”) size class. Some assumptions of the method are explored. Confidence intervals indicate that with few exceptions, estimates of exploitation rate have not changed over the time period of available data (1999-2009). The CCIR estimates should be viewed as an index of exploitation.
The application of the Reference Points (RPs) to lobster fisheries in LFAs 27-33 is discussed in the context of Canada’s precautionary approach and the current IFMP for LFAs 27-38. Options for RP development are provided. The candidate RPs in the most recent IFMP for LFAs 27-38 are based on landings from 1984-2004. Additional indicators of abundance are needed to develop RP. An abundance index for pre-recruits and commercial sizes based on FSRS catch rates is feasible for some assessment units. Recommendations for further development of RPs are provided.
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