Have discarding practices changed?
Indicators: Ratio of Discards to Landings | Bycatch
Based on all three methods used to analyze the ratio of discards to catch, the lowest discard rate for all years of the baseline period and the catch share program occurred in 2011. However, that low point was followed by an increase in 2012. The ratio of discards to catch, when summed over all stocks, showed no discernible trend during the baseline period. But the three lowest values for the ratio happened during the first three years of the sector program. The average ratio of discards to landings exhibited an increasing trend during the first part of the baseline period. This trend appeared to reverse after 2007, however. In 2011, the average discard ratio was at its lowest point of all years observed in baseline or catch share periods. The trend in median discard fraction was generally similar to that of the average discard fraction. However, there were important limitations to the data available prior to 2009. These limitations make it difficult to interpret trends and compare discard ratios between baseline and Sector periods.
This indicator measures the fraction of caught fish that are discarded by fishing vessels, by species.
Baseline: Before Catch Share Program
The data from the baseline period describe the discard ratios in a way that is comparable to data from the Sector Program. We attempted to calculate discard fractions for the large-mesh trawl to avoid confounding influences of discards in other fisheries (e.g., recreational, scallop and gillnet). Because of limitations in the data we examined, however, estimates of discard fractions are not consistent across stocks. Some represent all U.S. commercial discards, while others represent ratios of large-mesh trawl to all-trawl catches (see Data Limitations and Gaps).
During the baseline period, the three types of analyses conducted on discard fractions, namely crude, average, and median, generally depict an overall increasing trend from 2002 through 2007. That period was then followed by a decline. One reason for the peak is that 2007 was the first year data were available for Georges Bank (GB) haddock. GB haddock had high overall discard rates in that year because of a large biomass of undersized fish in the ecosystem at that time. Meanwhile, the large decline from 2007 to 2008 is because of the plentiful 2003 haddock cohort reaching a sufficient size to be landed. This trend was apparent for all three haddock stocks: Eastern GB, Western GB and Gulf of Maine (GOM). For the 15 stocks for which we have data from 2002 through 2009, 10 had an overall increasing trend in discard ratio while five had a declining trend. Of the increasing trends, the strongest were observed for the three yellowtail flounder stocks. Increased discards in these stocks is thought to be a result of restrictive trip limits imposed between 2004 and 2008. Redfish and GOM cod had the steepest reductions in bycatch during the baseline period.
During Catch Share Program (2011–2017)
The aggregate discard ratios show no apparent trend since 2010. However, 2011 had the lowest crude discard fraction, average discard fraction, and median discard fraction of any year from 2002 through 2012. That said, the discard fraction estimates are not directly comparable between the pre- and post-sector periods (see Data Limitations and Gaps). The increase in discard fraction in 2012 is partly result of the large 2010 haddock year class, which had grown to a size where they composed a large portion of the biomass in the ecosystem but were not of sufficient size to be landed. The highest discard fraction during the sector program was for Eastern GB cod, which had a discard fraction (discard to catch) of 0.45 in 2012. The most recent stock assessment for this stock indicated that recruitment was above recent average conditions in 2010, which may have contributed to the high discard ratios in 2012.
Data Gaps and Limitations
We sought to facilitate comparisons across stocks and between the sector and baseline periods by estimating the discards and landings. Time series data for landings and discards were not generally available across the same subset of fishing vessels, particularly during the baseline period. In many cases it was not possible to precisely distinguish discards from the Sector Program from other fishing programs in New England. For 10 stocks, data were sufficient to estimate the ratios of large-mesh trawl discards to all trawl catches. For four stocks, we could estimate ratios of discards to catches for all U.S. fisheries. And for two stocks, we could estimate ratios of large-mesh trawl discards to all U.S. commercial catches. For two stocks—cod and haddock on Eastern GB—discards and landings were presented in assessment documents only to the nearest 100 mt. We note that estimates for 2011 and 2012 are most robust because they are based on estimated landings and discards of fisheries operating in the Sector Program only. For GB haddock, gear-specific discards were available only from 2007 through 2012.
Finally, discards are estimated using statistical models that relate landings to discards based on observed trips. Without 100 percent observer coverage (Northeast Observer Coverage), these estimates have limited precision and unknown accuracy. In particular, the discarding behavior of fishermen may change when observers are on board.
Discard estimates were compiled from two sources: stock assessments and the commercial sector summaries from the Greater Atlantic Regional Fisheries Office (2011-2013): http://www.nero.noaa.gov/ro/fso/MultiMonReports.htm. All others taken from stock assessment documents.
Updated: February 2014
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