The isotopic differences and implications for Pacific razor clams along the Washington coast

Yongwen Gao,Joseph Gilbertson,Hongyan Zhang,O Chudaev,O Shouakar-Stash,R Harmon,Y Kharaka,R Millot

doi:10.1051/e3sconf/20199812005

Yongwen Gao, Joseph Gilbertson + Show 6 more

Open Access

https://doi.org/10.1051/e3sconf/20199812005

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Abstract

The Pacific razor clam fishery in Washington State has been co-managed by the coastal Indian Tribes and the state, but little is known about the growth and population structure of the clams due to difficulties of tagging and monitoring. Here we report the results of a pilot study using stable isotope ratios (δ13C and δ18O) of razor clam shells collected in two groups (juvenile vs. adult) and from two sites (Kalaloch Beach and Roosevelt Beach) where distinct biological differences in clam growth and survival rates were observed. The δ13C values of razor clam shells ranged from -2.9 to -0.3‰, whereas δ18O values of the same samples ranged from -2.2 to +1.4‰. Between the two sites there were significant differences in δ13C values especially for juvenile clams. The δ18O profiles from two representative shells demonstrated similar patterns of rapid growth as juveniles and seasonal patterns throughout the life span. Profiles of δ13C were sinusoidal but did not show seasonality and signatures of ocean acidification. We concluded that stable isotope analysis of razor clam shells is a potential new tool in shellfish research and management.

Highlights

Pacific razor clam, Siliqua patula (Dixon, 1789), is an important shellfish species distributed along the United States west coast from Pismo Beach in southern California to the Aleutian Islands in Alaska [1]
The total allowable catches (TACs) are set by applying a variable harvest rate to the total number of clams over 7.6 cm, and are divided by agreement between the Washington Department of Fish and Wildlife (WDFW) and the coastal Indian Tribe comanagers
We report stable isotope analyses ( 13C and 18O) on Pacific razor clam shells from two sites (Kalaloch Beach and Roosevelt Beach) and in two groups collected at a similar time

Summary

Introduction

Siliqua patula (Dixon, 1789), is an important shellfish species distributed along the United States west coast from Pismo Beach in southern California to the Aleutian Islands in Alaska [1]. Differences have been observed between Kalaloch Beach and the south adjacent Roosevelt Beach with respect to “harvestable” adult clam density and young of year clam density in recent years (WDFW, Hoh, and Quinault, unpublished management data). These differences resulted in diminished harvest that reduced harvest opportunity at Kalaloch Beach and had negative impacts on tribal member’s ability to exercise reserved Treaty-rights for shellfish and recreational opportunities for non-tribal harvesters. To the authors’ knowledge, no studies have tested these hypotheses and little is known about the population structure of razor clams due to difficulties to implement “tag and recover” programs [1] in the field

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