Compared to the control net (zero slack), there was no significant difference in winter flounder catch/ escapement across all 6 experimental variations in headrope slack.

For the purposes of this proof of concept study, however, we elected to use all of the available data generated and combined all bottom dwelling fish under the term of “demersals”.  This category includes winter flounder, summer flounder, other flounders, and all species of skates.  We did this under the premise that they will display similar response behaviors to towed nets as winter flounder since they primarily dwell on the sea floor.  We further reduced the six levels of slack to a single level (experimental) and compared it with the control (zero slack) in an effort to improve statistical analysis.  Analyzing this combined data set of “demersals” showed a significantly lower catch of all these species with headrope slack compared to no headrope slack.  Increasing slack beyond zero increases the escapement of this combined set of species.  We speculate that this effect may also be indicative of the response for winter flounder had they been encountered in greater numbers thus allowing the data set to be more robust. 

Data analysis of the squid catch showed a significant reduction in total catch in the experimental net compared to the control net. This is obviously not the result we were hoping for and additional net testing is needed to better determine the particulars of this result.

We also looked at another combined data set called “crustaceans”.  Crustaceans included lobsters, all true crabs, and horseshoe crabs.  This combined data set showed a significant difference in total catch of crustaceans between the experimental and control nets.  The experimental net had lower totals of crustaceans. This indicates an additional benefit for the drop chain sweep, a reduction in crab totals equates to reduced crew effort relative to sorting the crab from the catch and has a possible ecological benefit as well.  

Catches of squid, combined demersals, and crustaceans were all statistically significant for headrope slack compared to the control net (zero slack). Catches of these species were reduced in the experimental net.

The limited data set produced by this proof of concept is not robust enough to determine which adjustment(s) of slack produced greater or less escapement of winter flounder, combined demersals, or squid. However at the 6” and 24” slack intervals there is no significant difference when compared to the control for squid catch. 

Using the plots of total demersal catch by increment provided evidence of increased reduction for total demersal species at the 24” level. This suggests optimum escapement of bottom dwelling fish at a 24” slack in the headrope. Similarly, using the plots of total squid catch by increment provided evidence of less loss of squid (larger catch) at both the 24 inch adjustment and the 6 inch adjustment. More replicate tows would allow for the determination of the optimal headrope slack that promotes winter flounder bycatch reduction while optimizing squid retention.