ICES WKSHARK REPORT Report of the Workshop on Splitting of Deep-water Shark Historical Catch Data (WKSHARK) 17 June Copenhagen, Denmark

Transcription

1 ICES WKSHARK REPORT 2011 ICES ADVISORY COMMITTEE ICES CM 2011/ACOM:36 Report of the Workshop on Splitting of Deep-water Shark Historical Catch Data (WKSHARK) 17 June 2011 Copenhagen, Denmark

2 International Council for the Exploration of the Sea Conseil International pour l Exploration de la Mer H. C. Andersens Boulevard DK-1553 Copenhagen V Denmark Telephone (+45) Telefax (+45) info@ices.dk Recommended format for purposes of citation: ICES Report of the Workshop on Splitting of Deep-water Shark Historical Catch Data (WKSHARK), 17 June 2011, Copenhagen, Denmark. ICES CM 2011/ACOM: pp. For permission to reproduce material from this publication, please apply to the General Secretary. The document is a report of an Expert Group under the auspices of the International Council for the Exploration of the Sea and does not necessarily represent the views of the Council International Council for the Exploration of the Sea

3 ICES WKSHARK REPORT 2011 i Contents 1 Executive Summary Introduction Terms of Reference Participants Background General introduction Historical catch composition Recent landings trends Surveys Data received Irish observer data Irish/Norwegian Gillnet retrieval Anglo-Spanish landings records UK observer data Other data Data analysis Analysis of UK observer data Main conclusions Proposed procedure Surveys Modelling and data requirements Possible model structures Future data requirements References Tables and figures Annex 1: Participants list... 20

4

5 ICES WKSHARK REPORT Executive Summary Several species of deep-water sharks are exploited in the ICES area. Centrophorus squamosus and Centroscymnus coelolepis have been the two species of greatest importance to commercial fisheries. The term siki is used in the fishing industry to describe a mixed category of deep-water sharks principally comprising Centrophorus squamosus and Centroscymnus coelolepis mixed with smaller quantities of other species. Centrophorus squamosus and Centroscymnus coelolepis have very different biological traits. However, for assessment purposes, ICES has in the past combined data from the two species. This is because landing data were combined for some of the main countries for most of the time since the beginning of their fisheries. This workshop was held to request historical catch data from various sources, and to examine these data to better split the catch data into its component species. New data were received from the UK, Ireland, Norway and Spain, from trawl, longline and gillnet fisheries. French data were provided after the meeting data, but was also examined. Initial examination of these data showed greater variation in catches than expected, with the proportion of C. squamosus to C. coelolepis varying considerably on both a temporal and spatial level. There were also differences between the new estimates of the proportion estimates and those previously adopted by WGEF to split the two stocks. Further information was required to better explain some of these differences and requests for greater resolution in the data were made in some cases. The analysis of the data available for some vessels showed evidence of relationships between the relative occurrence of these species and bottom features, such as seamounts and ridges. These can be used to extrapolate which species were caught based on known topographic and depth preferences of C. squamosus and of C. coelolepis. While further information was received it was not possible to analyse these data in the short term. Further analysis will take place before WGEF 2012.

6 2 ICES WKSHARK REPORT Introduction 2.1 Terms of Reference 2010/2/ACOM36 The Workshop on splitting of deep-water shark historical catch data WKSHARK (WKSHARK), chaired by Graham Johnston, Ireland, will meet at ICES Headquarters, 17 June 2011 to: a ) Compile of the available information on siki by fishery: i ) Deep-water trawl fisheries; ii ) Longline fisheries; and iii ) Gillnet fisheries. Preferentially data should be made available on a haul by haul basis together with geographical information of the haul. b ) Adopt an agreed statistical procedure to analyse the data and on splitting ratio estimators by fishery; c ) Split ratio estimates for each fishery together with a summary with the assumptions and criteria adopted, as well as, the main uncertainties or weakness of the estimates. The Workshop will provide a draft report by 20 June 2011 to WGEF and a final report by 3 July 2011 for the attention of ACOM. 2.2 Participants Graham Johnston (Ireland) Ivone Figueiredo (Portugal) Jonathan White (Ireland)* Nils-roar Hareide (Norway)* Pascal Lorance (France)* Phil Large (UK)* Tom Blasdale (UK) *By correspondence 2.3 Background Several species of deep-water sharks have been exploited in the ICES area. Centrophorus squamosus and Centroscymnus coelolepis have been the two species of greatest importance to commercial fisheries. The term siki is used in the fishing industry to describe a mixed category of deep-water sharks principally comprising Centrophorus squamosus and Centroscymnus coelolepis mixed with smaller quantities of other species. Centrophorus squamosus and Centroscymnus coelolepis have very different biological traits. However, for assessment purposes, ICES has in the past combined data from the two species. This is because landing data were combined for some of the main countries for most of the time since the beginning of their fisheries. The 2010 Deep-water Benchmark Workshop (WKDEEP) examined assessment methodologies for these species and concluded that assessment using combined data was inappropriate to evaluate the stock status of each species. WKDEEP concluded that efforts should be continued to split the historic combined landings series into its individual species components (ICES 2010a). The main goal of this workshop is to better collate and estimate catch data at species level.

7 ICES WKSHARK REPORT General introduction Historical catch composition Two species of deep-water shark, Centrophorus squamosus, the Leafscale gulper shark, and Centroscymnus coelolepis, the Portuguese dogfish, make up the largest part of the combined category that has traditionally been referred to as siki sharks. During the deep-water fishery that took place in the 1990s and early 2000s, in some cases these were landed separately by species, but more usually, were landed together. These two species have different life histories and, in general, are found at slightly different depths; therefore stocks could be affected at different rates by deep-water fishing. Assessment of these two species is difficult without accurate landing records that can show the actual numbers of the species in the catch. ICES Working Group on Elasmobranch Fishes (WGEF) first attempted to separate the landings of these species into their components in 2006 (ICES 2006). Certain assumptions were made on their relative proportions based on data available at the time. These data included: Official logbooks; Skipper s private logbooks; Deep-water survey results, both trawl and longline; Observer trips; The proportions of the two species found during gillnet retrieval surveys. These proportion estimates were then applied to the siki shark landings category for different countries and years, as shown in Table 1. The composition of generic landings was also estimated based on the criteria adopted in 2005 WGEF. The allowed a split of all generic elasmobranch nei landings from the Northeast Atlantic in the period (Figueiredo et al., WD 2005) Recent landings trends There has been a decrease in deep-water fishing since 2006, with a restriction on the use of deep-water gillnets coming into force in 2007, and a complete ban in The current TAC for most deep-water species is set at zero. It was felt that it was appropriate time to revisit these calculations and attempt to better assess the ratio of the two shark species in the landings (ICES 2010b). With no current commercial fishing, and with the cessation of certain national deep-water surveys, there are few sources of information other than historical records. This workshop was formed to collate new information from national institutes and fishing organizations (through the Regional Advisory Councils), as well as to examine statistical methods for applying new ratios to the historical landings figures Surveys In addition, a review was carried out of results from Scottish and Irish deep-water surveys (Dobby et al., 2010). While it had not been intended to look at survey data outside the Bayesian model approach during this workshop, it was felt that this study could potentially be further used to analyse the historical commercial data (see Section 5).

8 4 ICES WKSHARK REPORT Data received New data on the ratio of the two siki shark species from commercial sources were provided before the meeting. These came from Ireland, the UK, Spain and a joint Ireland/Norwegian project. Details on each of these are provided below. 3.1 Irish observer data Data were provided from one combined scientific\commercial trip on board a commercial trawler. The target fish was orange roughy over seamounts in ICES Subdivision VIIc in February Commercial tows took place on the flats ; flat ground at the Porcupine Bank. Three tows caught Centrophorus squamosus or Centroscymnus coelolepis. 35 C. squamosus were caught, with just one C. coelolepis. Number of Centrophorus squamosus and Centroscymnus coelolepis observed during one Irish observer trip. Average Depth Centrophorus squamosus Centroscymnus coelolepis Haul Haul Haul Haul Haul Irish/Norwegian Gillnet retrieval Data were provided from a gillnet retrieval survey carried out by Ireland and Norway in Nets were retrieved from the Rockall (ICES Subdivision VIb) and Porcupine (ICES Subdivision VIIk) areas. Within the Rockall area, two fleets of nets were retrieved. One from 420 m did not contain either of the two siki shark species, while one retrieved from 720 m contained one C. squamosus. Within the Porcupine area one fleet of nets was recovered from 1050 m. This contained 199 C. squamosus and five C. coelolepis. In addition one Greenland shark, Somniosus microcephalus, was also identified in the nets from this fleet. Number of Centrophorus squamosus and Centroscymnus coelolepis retrieved from gillnets during Irish/Norwegian net retrieval survey. Area Depth Centrophorus squamosus Centroscymnus coelolepis VIb VIb VIIk Gear retrieval surveys can be a source of information from areas where other sources of commercial information may not be available. They have previously been used (ICES 2006) to provide indications of the proportions of the siki species within the catch. However, commercial observer data are preferable as the condition of fish in the nets after prolonged soak times, and subsequent identification/sampling may be problematic.

9 ICES WKSHARK REPORT Anglo-Spanish landings records Data were supplied to ICES by the South Western Waters RAC following their participation as observer to the 2010 deep-water benchmark meeting (WKDEEP). The data comprised total annual landings of deep-water shark species from five UK registered gillnetters belonging to the Fleetwood Fish Producers Organisation (FPO) for the years 2003 and Collectively, these five vessels accounted for 33% of total UK landings of deep-water sharks in 2003 and There is considerable inter-vessel and interannual variability within the data (see below). While all of the vessels reported landings of C. squamosus, C. coelolepis and Deania calceus, some vessels additionally reported minor landings of Centrophorus granulosus and Dalatias licha. This variation may result from species misidentification, however, since C. granulosus and D. licha typically have a more southerly distribution, it may also indicate differences in the areas fished. Cross checking the data against UK landings data proved inconclusive in validating the data. The working group therefore considered that no further progress could be made with this dataset unless it is supplemented with additional information on the location of the catches. Working group members will continue dialogue with the RAC with the aim of validating the present data and of improving the quality data available to future meetings of WGEF. Total landings (tonnes live weight) and proportion of total (in brackets) of deep-water sharks landed by vessels from the Fleetwood FPO, Vessel 1 vessel 2 vessel 3 vessel 4 vessel C. coelolepis 74.7 (0.47) (0.40) (0.64) (0.28) C. squamosus 65.8 (0.42) (0.60) 82.0 (0.36) (0.54) D. calceus 2.7 (0.02) 5.0 (0.01) 0.8 (0.00) 11.9 (0.02) E. spinax 7.3 (0.05) 38.2 (0.08) C. granulosus 3.5 (0.02) 34.3 (0.07) D. licha 4.3 (0.03) 0.4 (0.00) 2004 C. coelolepis 94.3 (0.39) (0.40) (0.78) 35.9 (0.47) (0.26) C. squamosus (0.48) (0.59) 83.7 (0.22) 14.9 (0.20) (0.67) D. calceus 9.2 (0.04) 8.3 (0.01) 8.4 (0.11) 27.8 (0.07) E. spinax 9.5 (0.04) 17.0 (0.22) C. granulosus 7.7 (0.03) D. licha 5.7 (0.02) 3.4 UK observer data A Working Document (Large et al., 2011) outlining the results from an observer programme on board UK-registered longliner and gillnetter vessels from 2004 to 2006 was presented to the group. This provided locations (by statistical rectangle) and quantities of different shark species landed. Table 2 summarizes the catches by species, gear type and location. Further analysis of this dataset is provided in the following chapter.

10 6 ICES WKSHARK REPORT Other data Data from France arrived after the meeting date, so complete analysis was not possible. Information received from France states that between the 1990s and 2001 all the French trawlers reported all catch of deep-water sharks as siki. It is also mentioned that in the 1990s only the larger deep-water sharks, i.e. Portuguese dogfish and leafscale gulper shark were landed. After 2001 some vessels began to sort the catches by species. It is considered that for the period , the leafscale gulper shark was properly identified however Portuguese dogfish and longnose velvet dogfish were both landed together and not distinguished by the industry. It is further referred that those two species are the only ones landed together because the other deep-water shark with commercial value, Centrocyllium fabricii, is sold and recorded separately as black dogfish. Observer data from was provided. Catch weights from 31 deep-water fishing trips were provided, along with the depth distribution of the catches of deepwater shark species. These showed a lack of consistency in the categories used each year, with C. squamosus, C. coelolepis and C. squamosus+ C.coelolepis, all being recorded, but in various quantities.

11 ICES WKSHARK REPORT Data analysis Initial analysis of the data caused some concerns. The initial analysis of observer trip data from longline and gillnet vessels showed high variability of the proportions of the two species in the catch. This implied that any application of splitting ratios to landings would need to take fishing area and depth into account, and that simply applying a ratio based on gear and/or vessel nationality is not a sufficiently robust procedure. Further analysis of these data appears to show marked difference in proportions depending on whether vessels were fishing over seamounts or not. This is level of resolution that is not generally provided to working groups, where landings are usually declared to ICES division. It was considered that these data may be available from the logbook systems in use at some national institutes. UK (England and Wales) observer data that helped determine the fishing locations by statistical rectangle for 2003 and 2004 was provided after a special request to Cefas. 4.1 Analysis of UK observer data Centroscymnus coelolepis (CYO) Centrophorus squamosus (GUQ) Main conclusions Longliner vs. Gillnet: there is a difference on the ratio of GUQ/(GUQ+CYO) between the two gears - Longliners tend to catch preferentially GUQ. Gillnet: fishing hauls at Vb and VIa tend to capture more CYO than GUQ while in VIb, VIIj and VIIk (excluding 25D7) tend to catch more GUQ. A spatial effect on the ratio is evident at more northern areas. CYO is more frequent in the hauls than in more southern areas. Longline: most of the 2005 fishing hauls, as well as all from 2006 took place at the continental slope to the west of Scotland and in the ratio GUQ/(CYO+GUQ) is high (>0.9). Longline: for hauls held in 2006 at the Anton Dohrn and Hebrides Terrace the ratio GUQ/(CYO+GUQ) was low (<.36). Such difference may reflect spatial distribution of Portuguese dogfish more related to special topographic features. Centroscymnus coelolepis (CYO)-comprised mostly females in almost all rectangles fished; Centrophorus squamosus (GUQ)- At Lousy Bank (located SW of the Faroe Islands and this area is thought to be part of the Rockall-Faroe micro-continent) catches are dominated by females while on the continental slope north of the Porcupine Seabight catches are dominated by males. The UK(E+W) observer dataset is currently under analysis by Cefas. The data supplied were only for use at the 2011 WKSHARK/WGEF meetings. 4.2 Proposed procedure The analysis of recent data available for this Workshop shows that the ratio estimates used before to split the siki landings could have introduced biases on the estimates of the landing by species. This may result from the fact they were estimated based on

12 8 ICES WKSHARK REPORT 2011 data not disaggregated by factors, recently identified as influential in the ratio estimation. Besides a fishing gear effect it was observed that conditionally to the gear used there is a spatial effect on the ratio estimates. The data provided by ICES division are considered inappropriate to the estimation and a lower level of discrimination is required. Depth was another factor considered to have an influence on the ratio estimate; C. coelolepis is more abundant at greater depths than C. squamosus (Hareide, pers. comm.). So if depth data by provided by fishing haul the precision of the ratio estimates will certainly be greatly improved. No temporal effects were considered because with the data available there was no evidence of year effect on the ratio estimates. Survey data (Dobby et al., 2010) may help resolve this issue. The data available at present are insufficient for update the estimates of historical or more recent siki landings per species (Table 1). Nevertheless, different procedures to apply in future were discussed if new data become available. In summary, it was considered that: the ratio differs between the two fishing gears; the species abundance ratio varies spatially; both species coexist spatially but there are differences on their relative abundance in catches as reflected on the ratio estimates.

13 ICES WKSHARK REPORT Surveys Work carried out in 2010, and presented to the ICES Annual Science Conference (Dobby et al., 2010) was examined to see if any changes in survey abundance could be used to explain differences in commercial catches. In particular, as the two siki species are found at different depth bands, changes in abundance would help explain geographic changes in relative abundance if these could be associated with slopes, banks or seamounts. This however was preliminary work on one species, and further analysis will be carried out before these methods are applied retrospectively to commercial catches.

14 10 ICES WKSHARK REPORT Modelling and data requirements As well as analysis of the data, several models were proposed to attempt to calculate the proportions in the catch (White, 2011). These approaches were discussed and assessed. The flowcharts below reflect the possible approaches to determining the ratio estimates according to the data sources available:

15 ICES WKSHARK REPORT Detailed Historical data DATA AVAILABLE Sources: 1. Trip Landings weight 2. Logbook 0 3.Skiper personal logbook INDIVIDUAL HAUL INFORMATION (1&2&3): - Year - Fishing gear - Day/Month - ICES rectangle - Species total weight OUTPUT 1. LANDING ESTIMATES BY: - SPEC IES - YEAR/MONTH - ICES RECTANGLE 2. SPECIES RATIO ESTIMATES BY: - YEAR/MONTH - ICES RECTANGLE

16 12 ICES WKSHARK REPORT Detailed Historical data for some years DATA AVAILABLE Sources: 1. Trip Landings weight 2. Logbook (some years) 3. Skiper personal 0 logbook (some years) INDIVIDUAL HAUL INFORMATION (2&3): - Year - Fishing gear - Day/Month - ICES rectangle - Total weight by species OUTPUT 1. SPECIES RATIO ESTIMATES BY: - YEAR/MONTH - ICES RECTANGLE - FISHING GEAR LANDING DATA INFORMATION (1): - Year - Fishing gear - Day/Month - ICES rectangle - TOTAL WEIGHT DEEP- Assumptions on how ratio estimates behave for cases for which detailed data are available OUTPUT 2. LANDING ESTIMATES BY: - SPEC IES - YEAR/MONTH - ICES RECTANGLE In the second case the assumptions made can be done: 1 ) based on expert judgment only; or 2 ) statistical modelling with either frequencist or Bayesian approaches. Using Bayesian approach estimation, as well as, and statistical testing are based upon frequency distributions of variables and the developed frequency distributions enable variables and their accuracies to be spread across all instances of data points, including those which are missing so enabling missing values to be accommodated and estimated. All estimates are provided with credibility intervals, akin to confidence intervals, so giving estimates not only of the values in question and their errors but also the shapes of the frequency distributions around estimates.

17 ICES WKSHARK REPORT According to the quality and quantity of the data available in the second case several models can be essayed. Under a Bayesian framework each model is hierarchical in structure, as this enables the transfer of estimators, in the form of means and precisions (calculated as 1/ sample variance), across variables. This transfer of knowledge (Ntzoufras, 2009) enables strength in estimators to be gathered and spread across data and parameters, lending weight to the mean, variance and shape of frequency distributions that are data (information) poor. 6.1 Possible model structures Model 1: Fixed effect year and region structure and fishing gear The Model will accommodate data discriminated by fishing gear and years and regions (at least ICES rectangles). The fixed effect component will give inference of influence of yearly contribution by region for each fishing gear. Model 2: State Space year and region structure and fishing gear Model 2 will accommodate incomplete data, i.e. there are data discriminated by fishing gear and years and regions (at least ICES rectangles) only for some periods of the time range. A solution to fill the blanks will be to estimate the probability of ratio using previous time-lag (it can be month or year depending on the size of the gap) in each region for each fishing gear within the confines of a common precision (1/variance). Model 3: Random effect ICES area by year State space development of probability of species catches for each fishing gear by ICES statistical rectangle for each year, enabling chronological evolution of the likelihood of species ratio. These model scenarios will be further evaluated in 2012.

18 14 ICES WKSHARK REPORT Future data requirements Further data will be provided from the UK (Cefas), which will give catch by species at a greater resolution than previously available. These catches will be examined prior to the 2012 WGEF meeting. A depth data by haul will allow to evaluate the influence of depth on the spatial distribution of ratio; the data available by the Cefas observer programme does not to allow disentangling the effect between the two gears used; if other sources of data confirm the spatially relationship of ratio GUQ/(CYO+GUQ) model can be proposed to map the spatial distribution of the ratio which can be further used to split the landings if those can be provided at least at ICES rectangle level. A request will be made to the SWWRAC to supplement the data already provided with some positional information on the catches. Species information will also be expanded to cover those declared landed to ensure there is no confusion with species names because of language (Table 3).

19 ICES WKSHARK REPORT References Dobby, H., Clarke, M., Johnston, G, Dransfeld, L., Kelly, C., Neat, F. and Jones, E Trends in abundance and distribution of deepwater sharks to the west of the British Isles from trawl surveys. ICES CM 2010/E:09. Figueiredo I., Bordalo-Machado, P., Gordo, L.S., and Moura, T WD. An overview of elasmobranch NEI landings from the north-east Atlantic in the period Working Document to WGEF. ICES Report of the Working Group on Elasmobranch Fishes (WGEF), June 2006, Copenhagen, Denmark. ICES CM 2006/ACFM: pp. ICES. 2010a. Report of the Benchmark Workshop on deepwater species (WKDEEP) February 2010., Copenhagen, Denmark. ICES CM 2010/ACOM pp. ICES. 2010b. Report of the Working Group on Elasmobranch Fishes (WGEF), June 2010, Horta, Portugal, ICES CM 2010/ACOM pp. Large, P.A., Readdy, L., Ashworth, J., Enever, R and Garrod, C Summary results and outcomes from UK (England and Wales) deep-water scientific observer trips, Working Document. 14pp. Ntzoufras, I Bayesian modelling using WinBUGS. Wiley series on Computational statistics. John Wiley & Sons publishing. 493pp. White, J Division of Siki catch to Portuguese Dogfish and Leafscale Gulper Shark in a Bayesian framework, Using OpenBUGS software - a program for Bayesian analysis of complex statistical models using Markov chain Monte Carlo (MCMC) techniques. Working document to WKSHARK 2011.

20 16 ICES WKSHARK REPORT Tables and figures

21 ICES WKSHARK REPORT Table 1. Description of how ratio of Centroscymnus coelolepis to Centrophorus squamosus was derived by WGEF 2006.

22 18 ICES WKSHARK REPORT 2011 Table 2. Summary of catches by area and gear from UK deep-water observer programme (Source: Large et al., 2011).

23 ICES WKSHARK REPORT Table 3. List of the commercial deep-water shark species landed, and their common names. Common name English French Spain (Basque) Spain (Galicia) Scientific Name Portuguese dogfish Centroscymnus coelolepis Leafscale dogfish Centrophorus squamosus Velvet belly Etmopterus spinax Gluper shark Centrophorus granulosus Kitefin Dalatias licha Birdbeak dogfish Deania calcea Longnose velvet dogfish Centroselachus crepidater Lantern sharn Etmopterus princeps

24 20 ICES WKSHARK REPORT 2011 Annex 1: Participants list Name Address Phone/Fax Tom Blasdale Joint Nature Phone Conservation Committee Inverdee House Baxter Street AB11 9QA Aberdeen United Kingdom Fax Ivone Figueiredo INRB - IPIMAR Avenida de Brasilia Lisbon Portugal Phone Fax ivonefig@ipimar.pt Niels Roar Hareide By correspondence Graham Johnston Chair Phil Large By correspondence Pascal Lorance By correspondence Jonathan White By correspondence PO Box 5 NO-6021 Aalesund Norway Marine Institute Rinville Oranmore Co. Galway Ireland Centre for Environment, Fisheries and Aquaculture Science (Cefas) Lowestoft Laboratory Pakefield Road NR33 0HT Lowestoft Suffolk United Kingdom Ifremer Nantes Centre PO Box 2 F Nantes Cédex 03 France Marine Institute Rinville Oranmore Co. Galway Ireland Phone Phone Phone Fax Phone Fax Phone Fax +353 nilsroar@online.no graham.johnston@marine.ie phil.large@cefas.co.uk pascal.lorance@ifremer.fr jonathan.white@marine.ie