Assessing Options for Using a Continuous Underway Fish Egg Sampler to Enhance Dedicated Daily Egg Production Studies Conducted from Small Research Vessels

ABSTRACT

This study was undertaken to identify options for using a Continuous Underway Fish Egg Sampler (CUFES) to enhance the application of the Daily Egg Production Method (DEPM) in situations where targeted surveys are conducted from small research vessels (e.g. <25m) and the time spent at each sampling site is short (e.g. <10 min). To do this, we conducted experiments to: 1) determine the reliability of information obtained from onboard examination of CUFES samples; 2) assess the sampling efficiency of CUFES while on-site and underway and 3) measure the effectiveness of underway CUFES samples in predicting the presence/absence of sardine eggs in the following CalVET net sample. We also compared the accuracy, precision and costs of estimates of total daily egg production obtained using data obtained from CalVET net samples taken at 1) predetermined sites (low and high sampling intensities) and 2) CUFES-determined sites. The accuracy of onboard estimates of egg abundance appeared to be affected by sea conditions. The efficiency of CUFES as an underway sampler was also lower when sea conditions were rough. Data from laboratory analyses of underway CUFES samples were a good predictor of egg abundance in the following CalVET net sample. Estimates of total egg production using CalVET samples from CUFES-determined sites based on laboratory analyses of CUFES samples differed by less than 10% from those obtained from pre-determined sites. However, estimates based on onboard analyses of CUFES samples differed from those obtained from pre-determined sites by up to 50%. When the time spent taking each CalVET sample is low (e.g. less than 10 minutes), using data from CUFES to reduce the number of samples taken using CalVET nets is not the optimal use of this technology. This is mainly because of difficulties associated with sorting plankton samples at sea, but also because in situations where the time spent at each site is short, the small decreases in field (cruise duration) and laboratory (sorting) costs do not outweigh the reductions in the reliability of estimates of egg production. However, CUFES data does appear to provide a potentially important source of information to increase the reliability of estimates of total daily egg production. Numerical techniques (e.g. analogous to integrated fishery assessment models) need to be developed to integrate data obtained from CUFES and CalVET nets to provide more accurate and precise estimates of total daily egg production for DEPM studies.