Feeding ecology of herring and mackerel in Icelandic waters

Transcription

1 Workshop on the Future Potential of Zooplankton and Mesopelagic Species October 1st - 2nd 2018, Reykjavík, Iceland Feeding ecology of herring and mackerel in Icelandic waters and other aspects of relevance for this workshop Guðmundur J. Óskarsson 11:20-11:40

2 Why focusing on pelagic fish considering the workshop s title? Large consumers on the zooplankton of interest Important components of the pelagic ecosystem that needs to account for when considering fishery on zooplankton.

3 Fish stocks in focus and their spatial and temporal distribution Stock Feeding period in Icel. waters Traditional fishing season Remarks Icelandic summerspawning herring Norwegian springspawning herring NE-Atlantic mackerel April-June and August-Sept. Oct.-Jan. Some bycatch in mackerel fishery (~10% of TAC) May-Sept. Aug.-Oct. Spawning, overwintering and nursery areas outside of Icel. waters June-Sept. July-Sept II

4 Icelandic summer-spawning herring The feeding grounds of Icelandic summer-spawing herring

5 Norwegian spring-spawning herring (Clupea harengus) Feeding grounds Based on results of International research surveys (e.g. IESNS and IESSNS)

6 Norwegian spring-spawning herring (Clupea harengus) Feeding grounds Based on results of International research surveys (e.g. IESNS and IESSNS)

7 NE Atlantic mackerel (Scomber scombrus) Feeding grounds Based on results of surveys (IESSNS) and Olafsdottir et al. (2015).

8 NE Atlantic mackerel (Scomber scombrus) Feeding grounds Based on results of surveys (IESSNS) and Olafsdottir et al. (2015).

9 Spawning stock biomass (mill. T) Spawning stock biomass (mill. T) Stock size and catchs 0,7 0,6 0,5 0,4 0,3 0,2 0, ,5 4 3,5 3 Icel. summer-sp. herring Year NE-Atlantic mackerel Total catches (thous. T) Norw. spring-sp. herring Year Total catches (thous. T) 2, ,5 1 0, Year ICES 2017

10 Stock size and catchs Icelandic catches since 1988 ICES 2017

11 Stock size and catchs Icelandic catches since 1988 ICES 2017

12 Stock size and catchs Icelandic catches since 1988 ICES 2017

13 Diet composition these three stocks in Icelandic waters Sampling locations in July 2010 and 2011 * Mackerel o Icelandic summer-sp. Herring Δ Norwegian sp.-sp. herring Óskarsson et al. 2015

14 Diet composition these three stocks in Icelandic waters Mackerel Herring * (mix.) * Óskarsson et al. 2015

15 Comparison to diet composition of blue whiting Pinnegar et al. 2014

16 D ie t w e ig h t (g ) Stomach content weight (mean ± 2 SE) 12 (a ) W SW SE E N (c ) W SW SE E N 12 (b ) A re a W SW SE E N Mackerel Herring Óskarsson et al. 2015

17 Total consumption of mackerel in Icelandic waters Derived from estimates of weight gain: Óskarsson et al. 2015

18 Total consumption of mackerel in Icelandic waters in 2010 Consumption Where: 1 Total, Y ( N A, Y WGain, A, Y ) ( CE) A N=stock number (in Icelandic EEZ on basis of IESSNS), W Gain =weight gain, A=age, Y=year, CE=conversion efficiency The estimates depends on assumptions of conversion efficiency (%) Year Total mackerel biomass in Icel. EEZ (thous. T) Total weight gain (thous. T) Food consumption (thous. T) (CE=10%) Óskarsson et al. 2015

19 Summary Three pelagic fish stocks that are major consumers of Calanus in Icelandic waters. Two of them are fished during their feeding season when occupying Icelandic waters, while the local stock during its overwintering (i.e. not feeding). Their stock size, geographical distribution and thereby fishing opportunities in Icelandic waters varies. Mackerel is apparently more effective Calanus feeder than herring more extensive feeding studies are in process.

20 Thanks for your attention 20