Population characteristics of the world's northernmost stocks of European lobster(Homarus gammarus)in Tysfjord and Nordfolda, northern Norway

Abstract

The northernmost self-sustaining populations of European lobster (Homarus gammarus) are found north of the Arctic Circle (66°33'N), in Tysfjord and Nordfolda, two large, deep, and relatively warm fjord systems in northern Norway. In contrast to most other Norwegian lobster populations, these genetically distinct populations are still found at relative high densities. This paper presents results from surveys conducted in the fjord systems in 1964-65 and between 1992 to 2005, and compares reproductive characteristics, morphology, growth, and catch-per-unit-effort (CPUE). The lobster population in Stefjord, one of four individual fjords in the Tysfjord fjord system, was characterised by a small mean carapace length (CL, 78±11 mm SD), and less than 18% of the catches were larger than the minimum legal size of 88 mm CL. Growth rates were also low, with an average increment per moult of 4.0 ± 0.9 mm CL for females and 5.6 ± 2.1 mm for males. The crusher claw increased on average 5.5 ± 2.3 mm at each moult in females, and 11.2 ± 7.6 mm in males. The smallest ovigerous female was 62 mm CL, and more than 60% of females above 66 mm CL were berried (egg-bearing). In contrast, lobster in the Nordfolda fjord system were larger, with more than 75% of the catch larger than minimum legal size, and M07099; Online publication date 24 February 2009 Received 30 November 2007; accepted 31 December 2008the smallest ovigerous female was 76 mm CL. Males in Nordfolda increased on average 8.3 ± 2.4 mm in CL at each moult. Lobster populations in the area of the midnight sun (24-h daylight during summer) were also morphologically different from lobster off southwestern Norway in crusher claw length for males and abdominal width for females. There were no differences in the size distribution or CPUE between the surveys in 1964-65 and between 1992 and 2005, leading to the conclusion that population density seemed to be relatively stable. The average density in the fjord systems of Tysfjord and Nordfolda was 155 ± 76 lobsters and average weight was 71 ± 26 kg per km shoreline in the main survey areas. The adaptation to a sub-arctic environment has resulted in geneticlly distinct populations as well as slightly altered biology and behaviour. Our assessment suggests that the populations are vulnerable to exploitation, and conservation plans should be elaborated.

A mark-recapture study of hatchery-reared juvenile European lobsters, Homarus gammarus, released at the rocky island of Helgoland (German Bight, North Sea) from 2000 to 2009

“…This density corresponds to a dive assessment in the field at the Northern rocky basement of 1.5 lobsters 100 m −2 (Schmalenbach, 2009a). In contrast, Steneck and Wilson (2001) reported up to 160 American lobsters 100 m −2 off the US-Mainecoast and in northern Norway the average density ranges from 9 to 19 European lobsters per 100 m shoreline (Agnalt et al, 2009). However, the sampling programme will continue at Helgoland and recapture numbers may further increase.…”

Deformities in larvae and juvenile European lobster (<i>Homarus gammarus</i>) exposed to lower pH at two different temperatures

“…gammarus is found along the continental shelf in the northeast Atlantic, which extends from the warm waters off Morocco to the colder areas near the Arctic Circle, i.e. Tysfjord and Nordfolda (68 • N) (Agnalt et al, 2009). This distribution covers a large latitudinal and temperature range.…”

Desktop study on autecology and productivity of European lobster (Homarus gammarus, L) in offshore wind farms

“…They possess two large claws, one blunt and designed for crushing and the other sharper and smaller normally used for slicing. Males have larger claws than females, females have wider abdomens (Agnalt et al, 2009, Sørdalen et al, 2018. Their exoskeleton is blue/navy on the dorsal side but slightly lighter underneath with an orange tinge.…”

“…However, their 'commercial range' is currently limited to northern France, Britain and Ireland. The northernmost populations are found in the Norwegian fjords Tysfjorden and Nordfolda, inside the Arctic Circle (Agnalt et al, 2009). In Norway and Shetland stocks have declined significantly or collapsed ( Figure 5).…”

“…In the Mediterranean and off the Iberian peninsula, north to the Bay of Biscay, lobsters are rare and generally well below commercial levels. Their stronghold, therefore, is a relatively small proportion of their previous commercial distribution (Holthuis 1991, Prodöhl et al, 2006, Phillips, 2013 (Schmalenbach, 2009); in British waters is 87mm 6 ; in Norwegian waters 88mm (Agnalt et al, 2009).…”