Differentiating between Sampling‐ and Environment‐Related Mortality in Shortnose Sturgeon Larvae Collected Using Anchored D‐Frame Nets. (24th May 2013)

• Record Type: Journal Article
• Authors: Usvyatsov, Sima; Watmough, James; Litvak, Matthew K.
• Is Part Of: North American journal of fisheries management. Volume 33:Number 3(2013)
• Page Start: 595
• Page End: 605
• Publication Date: 2013-05-24
• Subjects: Fishery management -- United States -- Periodicals; 333.956097305
• DOI: 10.1080/02755947.2013.785995
• Languages: English
• ISSNs: 0275-5947

Abstract

Abstract: This study provided the first attempt to differentiate between environmental‐ and sampling‐related mortality in larval Shortnose Sturgeon Acipenser brevirostrum . Anchored D‐frame nets are widely used for sampling sturgeon larvae, but the associated larval mortality rates are not known. We assessed larval mortality (1) by examining the effect of net deployment period on mortality rate; (2) directly, by deploying live larvae in nets and observing survival over time; and (3) indirectly, by establishing the time of larval death based on body decomposition. Larval mortality in nets deployed for 12 and 24 h was similar: 50% of the nets contained no live larvae. After a 6‐h deployment, half of the nets contained 60% or more live larvae. After placement of live larvae in nets for 12 h, the nets retained 60.0 ± 20.4% (mean ± SE) of the deployed larvae. Of the retained larvae, only 6.5 ± 2.3% (mean ± SE) survived 12 h inside the net. Decomposition rates of dead larvae were examined both in a controlled environment and in the nets. Dead larvae that were deployed in nets decomposed faster than those in a controlled environment, with high decay after only 12 h of deployment. A discriminant function analysis differentiated well between larvae that had been dead for 9 h and larvae that had been dead for 21 or 32 h. The assessment of time of death based on decomposition was used to identify the cause of mortality for Shortnose Sturgeon larvae collected in the Saint John River, New Brunswick, during 2008–2010. We propose that in short to medium deployment periods (up to overnight), pristine and partly decayed larvae can be assigned to sampling mortality, while highly decayed larvae can be assigned to environment‐related mortality. Using this distinction, sampling and environmental sources of mortality accounted for at least 20–56% and 4–25%, respectively, of the sampled Shortnose Sturgeon larvae. Received June 13, 2012; accepted March 7, 2013