Specific Objective 2 Sov 6 Paulus Et Al. 2016
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SoV 2.6 REPUBLIC OF NAMIBIA MINISTRY OF FISHERIES AND MARINE RESOURCES DIRECTORATE RESOURCE MANAGEMENT Cruise Report No 1/2016 RV Mirabilis Surveys of the Hake Stocks Survey No. 2016901: 11 January – 21 February 2016 Compiled by S. Paulus, Johannes Kathena ,Tobias Endjambi, Ester Nangolo A. van der Plas & P. Kainge National Marine Information and Research Centre (NatMIRC) Swakopmund, 2016 1 Hake Research, Demersal Subdivision National Marine Information and Research Centre (NatMIRC) P.O. Box 912 Swakopmund Namibia 2 TABLE OF CONTENTS Abstract ............................................................................................................................................. 5 1. Introduction ................................................................................................................................... 6 1.1 Background .............................................................................................................................. 6 1.2 Objectives ................................................................................................................................ 7 1.3 Participation ............................................................................................................................. 7 1.4 Narrative .................................................................................................................................. 8 2. Materials and Methods ................................................................................................................ 10 2.1 Introduction ........................................................................................................................... 10 2.2 Trawl and vessel equipment .................................................................................................. 10 2.3 Survey design ........................................................................................................................ 11 2.4 Data recording ....................................................................................................................... 11 2.5 Data analysis .......................................................................................................................... 12 2.5.1 Biomass estimates……………………………………………………………………….12 2.5.2 Species Distribution……………………………………………………………………..13 2.5.3 Size composition………………………………………………………………………...13 2.5.4 Recruitment estimates………………………………………………………………...…13 2.5.6 Hydrography…………………………………………………………………………….14 3. Results and Discussion? ...................................................................................................... ……15 3.1 Biomass estimates .................................................................................................................. 15 3.2 Species distribution ................................................................................................................ 18 3.3 Size composition .................................................................................................................... 20 3.4 Recruitment estimates ............................................................................................................ 22 3.5 Some Biological parameters .................................................................................................. 23 3.6 Environmental parameters ..................................................................................................... 25 4. Survey trends of some by-catch species (1990-2016) ................................................................. 28 4.1 Introduction ........................................................................................................................... 28 4.2 Kingklip ................................................................................................................................. 29 4.3 West Coast Sole ..................................................................................................................... 30 4.4 Dentex .................................................................................................................................... 31 4.5 Angel Fish (Atlantic Pomfret) ............................................................................................... 32 4.6 Horse Mackerel ...................................................................................................................... 33 4.7 Jacopever ............................................................................................................................... 34 4.8 Cape Monk ............................................................................................................................ 35 4.9 Snoek ..................................................................................................................................... 36 4.10 Flying Squid ........................................................................................................................ 37 4.11 Alfonsino ............................................................................................................................. 38 4.12 Cape Gurnard ....................................................................................................................... 39 4.13 Deep-sea Red Crab .............................................................................................................. 40 5. Acknowledgements ..................................................................................................................... 42 6. Literature cited ............................................................................................................................ 43 Appendix 1 – Trawl configuration .................................................................................................. 45 Appendix 2 – Areas ......................................................................................................................... 46 Appendix 3 – Gonad maturity stages classifications. ...................................................................... 46 Appendix 4 – Biomass estimates for the hakes since 1990. ............................................................ 47 Appendix 5 – Specifications for the vessel used in the research surveys of hake ........................... 48 Appendix 6 – List of survey stations and catch compositions (kg/hr) ............................................ 49 Appendix 7- Intercalibration Report ............................................................................................... 76 3 4 Abstract The research vessel (RV) Mirabilis was used to conduct the hake swept-area biomass survey from the 11th of January until the 21st of February 2016. A total of 216 trawl stations were conducted during the survey, covering the bottom depths between 88 and 682 m. The total hake biomass decreased by 10% (1 115 000 to 1 109 000 tonnes) between January/February 2015 survey and January/February 2016 survey. The non-fishable biomass has increased by 2%, while the fishable biomass decreased by 32%. The total biomass index of M. capensis decreased by 1.8% from 839 000 to 824 000 tonnes between 2015 and the 2016 estimates and its non-fishable biomass has increased by 17% while the fishable biomass has decreased by 36%. The total biomass of M. paradoxus has decreased by 33% (from 276 000 to 185 000 tonnes). The fishable biomass of that species has decreased by 15% and the non-fishable also decreased by 43%. The recruitment of M. capensis detected during the 2016 survey (the 2014 year class) were around 6.6 billion fish, above the long-term average. Areas of high density concentrations for M. capensis (>30 t/NM2) were found almost along the whole Namibian coast, except south of south of 28°S. The deep-water hake (M. paradoxus) was found in the deeper waters, with highest concentrations of densities (>30 t/NM2) found around Lüderitz and around Mowe Bay and Ambrose Bay. Intercalibration results showed that the catches for M.paradoxus were similar between the two vessels whereas Mirabilis caught more M.capensis overall because of two very large catches. Test for differences between length frequencies showed there were significant differences but for very low p-values, M.capensis (p = 4.134e-08) and M.paradoxus (p= 0.006512). The oceanographic conditions during the January/February 2016 hake survey reflected strong surface warming due to the generally weak southerly winds as well as strong summer insolation. Bottom temperatures over the shelf were also warmer than average in the north but average over the southern Namibian shelf for the summer period. The bottom low-oxygen waters were widespread over the inner shelf of most of the Namibian coastline and even impinged onto the outer shelf region. 5 1. Introduction 1.1 Background Namibian hake biomass surveys have been conducted since 1990. Up to 1999, the Norwegian research vessel, Dr. Fridtjof Nansen (Nansen), was used to conduct these surveys. In 1998 and 1999, the Nansen and Namibian commercial trawlers did parallel surveys, using the same trawl gears and applying the same methods, in order to enable inter-calibration between the commercial trawlers and the Nansen time series data. Namibia took over the responsibilities for conducting the hake biomass surveys with commercial vessels, as from 2000 (Table 1.1). Inter-calibration, through parallel trawling, between commercial vessels and Nansen were carried out each time a new commercial vessel