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Research Document - 2000/167

Evaluation of Horse Clam Stock Dynamics for a Directed Subtidal Horse Clam (Tresus capax and Tresus nuttallii) Fishery in British Columbia.

By Z. Zhang and A. Campbell


Biological information essential for addressing ecological concerns, assessing population stock dynamics, and evaluating fishing strategies for a directed fishery proposed for horse clams were examined. The depth distribution of horse clams appeared to extensively overlap with geoducks in the subtidal zones. The possible detrimental effect caused by horse clam exploitation on geoduck populations is, at present, unknown and should be examined in the future. The current depth restriction for horse clam and geoduck fishing, which is shallower than 10 feet (3.06 m) below chart datum, appears to be inadequate to sufficiently protect the eelgrass habitat in some areas. A general survey protocol was outlined for obtaining biological and ecological information, such as horse clam biomass, natural mortality rate, growth, and eelgrass distribution. A computer stochastic model was developed to evaluate the effect of alternative fishing schemes and exploitation rates on the reproduction potential of horse clam populations, based on known natural mortality and growth rates and age at vulnerability to fishing. Highly precautionary biological reference points were recommended for the initial phase of the directed fishery.

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