Subscribe
Click here to read the full report.
Proportion of trips sampled by year, quarter, area, and gear stratum are given in Table 1, while coverage for all strata is given in Table 2. Proportion covered in strata ranged between 0.08-0.26 by trip and 0.09-0.25 by weight, however many strata have little or no coverage particularly with regards to certain gear types (Table 1). Overall coverage was highest in 2005 (0.26) and lowest in 2007 (0.08)(Figure 2). It should be noted that in 2006 the observer project concentrated on only single and paired midwater trawls, and had no observations of purse seine gear in that year.
Percent occurrence of trips categorized by river herring bycatch expressed as a percentage of Atlantic herring landings is shown in Figure 3. Nearly 70 % of the observed trips had zero river herring bycatch. About 97% of the trips had < 2.5% bycatch of river herring, while <1% of the trips had bycatch >10%. This suggests that while incidents of river herring bycatch are low, they can be substantial given the high volume nature of the Atlantic herring fishery.
Most bycatch occurred near Cape Cod (GB/CC) and SNE in the late fall through spring periods (Figure 4). Specifically, large bycatch of river herring was observed in the areas of Cape Cod and Cape Ann, MA (WGOM), Nantucket (SNE) and the area around Block Island (SNE) (Figure 5-8). Bycatch was also observed near Cape Ann (WGOM) in the fall (Quarter 3). Highest bycatch of river herring occurred in the SNE area, particularly in 2007 near NJ (Figures 4).
Estimates of river herring bycatch were highest in the late fall and winter periods (Quarters 1 and 4: Figure 9). During this time, Atlantic herring, Atlantic mackerel, and river herring can be found together in mixed aggregations during their fall migration around Cape Cod, as well as during the overwintering period from Block Island south.
Overall, bycatch was highest in both single and paired midwater trawl gears, while it was lowest in purse seines. Surprisingly, bycatch was high in bottom trawls in 2007 (Figure 10). Catch of Atlantic herring are usually only 3-7,000 mt for bottom trawls compared to 50-60,000 mt for single and paired midwater trawls; thus, the high bycatch possibly indicates a higher encounter rate of river herring for bottom trawls.
It is important to note that the lack of large bycatch estimates for purse seines may not reflect the gears’ inability to catch river herring. Rather, purse seines are not currently operating in areas and seasons where the vast majority of estimated river herring removals occur (Figure 8).
Variation among yearly estimates of bycatch was high. The estimate of bycatch in 2007 (1.7 million pounds) was about an order of magnitude higher than the estimates of bycatch in 2005 (0.28 million fish) and 2006 (0.17 million fish)(Table 2). The increase was due mostly to high estimates during quarter 1 of 2007 across most gear types and areas (Figures 9 and 10). This suggests that the increase may be due to availability rather then a sampling artifact. The coefficients of variation (CV) of the bycatch estimates were also high and were not reduced with more intensive sampling (Table 2).
Estimates total yearly bycatch of river herring in the Atlantic herring fishery are similar to the levels of landings observed in the directed river herring fishery (ASMFC, 2008). However further analysis is need to determine if other small mesh fisheries (i.e. scup, squid, mackerel, and others) contribute as much or more to the estimates carried out in this analysis. This study suggests that any small mesh fishery operating in the SNE and GB/CC area in the late fall to early spring may also have significant river herring bycatch
The use of both observer and portside data allowed for the estimation of total bycatch of river herring in the directed Atlantic herring fishery. Further analysis is needed to determine if purse seine operations would encounter river herring should they start fishing in areas or seasons where river herring may occur. Also, the directed Atlantic herring fishery is under going profound management changes (e.g., available quotas by management area, allowable gear types, etc.) and they should be made with some consideration of the impact on river herring bycatch.
Funding for both sampling programs should continue and the coverage of the directed Atlantic herring fishery should increase to continue to provide precise estimates of river herring bycatch for management use. Additionally data from both projects can also be used to examine bycatch issues for other small bodied fishes (i.e. shad, dogfish, haddock, and whiting).