Eastern Sea Fisheries Joint Committee Research Report 2010 Rw Jessop S
Total Page:16
File Type:pdf, Size:1020Kb
EASTERN SEA FISHERIES JOINT COMMITTEE RESEARCH REPORT 2010 R. W. JESSOP S. HINNI J. SKINNER J. R. WOO CONTENTS 1.0 SUMMARY … … … … … … … … … … … … … … … … … … 1 MUSSEL ( Mytilus edulis ) RESEARCH 2.0 Wash Mussel Stocks … … … … … … … … … … … … … … … … … … 3 2.1 Summary … … … … … … … … … … … … … … … … … … 3 2.2 Method … … … … … … … … … … … … … … … … … … 4 2.3 Results … … … … … … … … … … … … … … … … … … 6 2.4 Discussion … … … … … … … … … … … … … … … … … … 35 2.5 Titchwell Marsh Mussel Bed … … … … … … … … … … … … … … … … 38 2.6 Sublittoral Mussels … … … … … … … … … … … … … … … … … … 51 COCKLE ( Cerastoderma edule ) RESEARCH 3.0 Wash Cockle Stocks … … … … … … … … … … … … … … … … … … 55 3.1 Summary … … … … … … … … … … … … … … … … … … 55 3.2 Method … … … … … … … … … … … … … … … … … … 56 3.3 Spring Survey Results … … … … … … … … … … … … … … … … … … 57 3.4 Autumn Survey Results … … … … … … … … … … … … … … … … … … 86 3.5 Discussion … … … … … … … … … … … … … … … … … … 96 3.6 Effects of Cockle Fishery on Benthic Organisms and Sediment … … … … … 99 CRUSTACEAN FISHERIES RESEARCH 4.0 Crustacean Fisheries … … … … … … … … … … … … … … … … … … 115 4.1 Introduction … … … … … … … … … … … … … … … … … … 115 4.2 Background to the stain test … … … … … … … … … … … … … … … … 116 4.3 Initial trials at ESFJC … … … … … … … … … … … … … … … … … 121 4.4 Prosecution case … … … … … … … … … … … … … … … … … … 122 4.5 Development of the method … … … … … … … … … … … … … … … … 123 4.6 Description of methodology and evidence requirements … … … … … … … 126 4.7 Further trials, training, and promoting the kit … … … … … … … … … … 128 4.8 The future of the test … … … … … … … … … … … … … … … … … … 129 ROSS WORM ( Sabellaria spinulosa ) RESEARCH 5.0 RoxAnn TM A.G.D.S Surveys … … … … … … … … … … … … … … … 131 5.1 Introduction … … … … … … … … … … … … … … … … … … 131 5.2 Method … … … … … … … … … … … … … … … … … … 132 5.3 Results … … … … … … … … … … … … … … … … … … 137 5.4 Discussion … … … … … … … … … … … … … … … … … … 167 PRODUCTIVITY RESEARCH 6.0 Study of the Wash Embayment Ecosystem and Productivity … … … 171 6.1 Introduction … … … … … … … … … … … … … … … … … … 171 6.2 Aim … … … … … … … … … … … … … … … … … … 172 6.3 Methodology … … … … … … … … … … … … … … … … … … 173 6.4 Results … … … … … … … … … … … … … … … … … … 176 6.5 Discussion … … … … … … … … … … … … … … … … … … 182 6.6 Aims of SWEEP 2011/12 … … … … … … … … … … … … … … … 184 SUFFOLK RIVERS SURVEYS 7.0 Suffolk Rivers Surveys … … … … … … … … … … … … … … … … … … 185 7.1 Introduction … … … … … … … … … … … … … … … … … … 185 7.2 Cockle Survey … … … … … … … … … … … … … … … … … … 185 7.3 Native Oyster Survey … … … … … … … … … … … … … … … … … … 194 7.4 Manila Clam Survey … … … … … … … … … … … … … … … … … … 199 7.5 Peacock Worm Survey … … … … … … … … … … … … … … … … … … 208 LUGWORM ( Arenicola marina ), SAND MASON ( Lanice conchilega ), and TELLIN ( Macoma balthica ) RESEARCH 8.0 Distribution of Arenicola , Lanice and Macoma in The Wash … … … 211 8.1 Introduction … … … … … … … … … … … … … … … … … … 211 8.2 Methodology and Results … … … … … … … … … … … … … … … … … 212 8.3 Discussion … … … … … … … … … … … … … … … … … … 220 BACTERIOLOGICAL SAMPLING 9.0 Bacteriological sampling 2006 … … … … … … … … … … … … … … … 222 9.1 Introduction … … … … … … … … … … … … … … … … … … 222 9.2 Methodology and analysis … … … … … … … … … … … … … … … … … 224 9.3 Results and Discussion … … … … … … … … … … … … … … … … … 225 10.0 Acknowlegements … … … … … … … … … … … … … … … … … … 226 11.0 References … … … … … … … … … … … … … … … … … … 227 1.0 SUMMARY The annual autumn mussel surveys found the stock of mussels on the intertidal sandbanks of the Wash to be 9,626 tonnes. Not only is this a significant decrease from the 15,188 tonnes recorded following the 2009 surveys, it means the stocks have fallen below the 12,000 tonnes Conservation Objective set for the site by Natural England. This decline greatly exceeded anticipated losses following the 2009/10 fishery, during which approximately 800 tonnes of mussels had been relayed from the intertidal beds into the several fishery. On some beds, such as the Gat, losses were as high as 60%. High numbers of gaping shells on several of the beds indicated recent mortalities were not just limited to older mussels but that large numbers two and three year old mussels had recently died, too. Although it is currently uncertain what caused the deaths, high numbers of the parasitic copepod Mytilicola intestinalis were found in mussel samples taken from several of the beds. Although it was not possible to open the intertidal mussel stocks to the 2010/11 fishery following their decline, two beds of sublittoral mussel seed were identified in February 2011. One, along the Lincolnshire Coast, near to the Lynn and Inner Dowsing windfarm was found to support very young seed that was too small for relaying. The other, however, situated along the Norfolk Coast, north of Mundesley, did support suitable mussels for a fishery. Although the stock on this bed was estimated to be approximately 22,000 tonnes, a large part of this bed was situated within the ESFJC 3-mile boundary in an area restricted to dredging. Following consultation with crab and lobster fishermen, to resolve potential gear conflict issues, it was possible to open 7,700 tonnes of these stocks to the mussel fishery. The spring cockle surveys found that the cockle stocks in the Wash had declined from 22,419 tonnes in 2009 to 16,256 tonnes. Apart from approximately 1,400 tonnes that had been harvested during the year by the handworked fishery, most of the losses were attributed to the atypical mortality that was first noticed to be occurring in the Wash in 2008. The cause of the mortalities is still unknown, but has resulted in the cockle stocks declining from their second highest recorded biomass in 2007 to a situation in which it has been difficult for the industry to find patches of adult cockles dense enough to fish. Because of the difficulties in identifying sufficient adult stocks that were discrete from juvenile stocks, the dredge fishery remained closed during 2010. Although the 29 vessels that participated in the handwork fishery exhausted the available TAC of 2,081 tonnes by December, several vessels were resorting to landing small cockles from Herring Hill by the end of the season. Following concerns that the practice of “propeller washing” associated with the handwork cockle fishery might be damaging the ecology of the site a study was conducted to assess the potential disturbance. Over a four-month period, core samples were taken from five rings created by propeller washing and compared with samples taken from five unfished control sites. Apart from expected changes in the abundance of cockles, no significant differences were found to either the infauna or 1 substratum between the fished and unfished sites, indicating the handwork fishery was not having an adverse impact on the site. The Committee has a byelaw prohibiting the removal of egg-bearing “berried” lobsters from the district. Identifying berried lobsters can be problematic, however, if the eggs have been forcibly scrubbed off before landing. Over the past five years, therefore, the Committee has developed a staining technique to facilitate the detection of scrubbed lobsters. The crustacean section of this report details the development of the staining technique and the blind trials that have been conducted to test its accuracy. Surveys have been conducted through the year to identify and map the distribution of Sabellaria spinulosa reefs. These surveys included monitoring five areas within the Wash that had been surveyed in 2009 and four additional areas along the Lincolnshire coast that had been subject to a broadscale survey in 2008. Data collected from these surveys, combined with past data, will help to identify core areas that have been found to regularly support reef features. Following the unexplained mortalities of cockles in 2008, ESFJC initiated a project to study the productivity of the Wash in case localised food limitations were a causal effect. Regular monitoring of chlorophyll levels have been conducted at several sites throughout the year, to determine whether shellfish stocks might be exceeding their localised carrying capacities. Because the several fishery lays have the highest concentrations of stock in the Wash, the majority of monitoring has occurred around these areas. Although analysis of the data have found the chlorophyll levels to be heterogeneous, the study has so far not detected any consistent reduction in Chlorophyll levels above the lays that could be attributed to the mussels’ filter feeding. These studies have concentrated on chlorophyll levels at 1m depth, however, which depending on states of the tide could be several metres above the mussels. Further studies are planned to measure chlorophyll levels closer to the seabed during 2011. Surveys conducted in the Rivers Stour and Orwell found cockle stocks along the banks of both rivers had increased slightly from their low levels the previous year, but were still much lower than levels recorded in 2001 and 2003. A small population of native oysters at Holbrook Bay was similarly found to have grown from the low levels recorded in 2009, but had not recovered to levels recorded prior to 2006. This population appeared to have spread, however, to a nearby area at Copperas Bay, where juveniles were found on a gravel bank. These surveys also investigated the distribution of Manila clams that had been identified in the