Atlantic wolffish (Anarhichas lupus) COSEWIC assessment and status report 2012: chapter 9
More is known about the biology of the Atlantic Wolffish than of the Spotted and Northern Wolffish, mainly because of its coastal distribution, which has also facilitated dive observations. Key studies come from Templeman (1984, 1985, 1986), McRuer et al. (2000), and Simpson and Kulka (2002). There are ongoing studies in Quebec (see Dutil et al. 2010, Lachance et al. 2010, Laroque et al. 2008). Laboratory studies have been done by Johannessen et al. (1993) and Lachance et al. ( 2010). Finally, a summary of the known aspects of the biology of wolffish was presented by Kulka et al. (2007).
In the waters off Newfoundland and Labrador, Templeman (1986) determined that the size at which 50% of females reach sexual maturity (L50) is 51.4 cm in the northern part of the range (Labrador Sea and eastern Newfoundland, NAFO Divisions 2GH+3K) and 68.2 cm in the southern part of the range (southern Grand Banks Div. 3NOPs). The difference could be related to variation in water temperature, which affects growth.
According to a growth curve constructed using the Gompertz function with individuals from the Gulf of Maine (Nelson and Ross 1992), the age at sexual maturity (A50) is approximately 8 years in the southern part of the range. Curves based on von Bertalanffy equations by McRuer et al. (2000) suggest the age at sexual maturity is between 10 and 15 years in the Scotian Shelf, based on data from Greenland by Beese and Kändler (1969) and from the Gulf of Maine by Nelson and Ross (1992). Some of the population parameters assessed by Templeman were based on specimens caught between 1946 and 1967, and they may not apply to recent populations.
A recent examination of the Canadian RV database on the Scotian Shelf revealed that, from 48 individuals of Atlantic Wolffish, all individuals less than 24 cm were immature, while all fish greater than 38 cm were mature, based on visual inspection of the reproductive organs (Simon et al. 2011). However, the low number of fish makes length at 50% maturity imprecise. Moreover some uncertainty about maturity staging of wolffish may have underestimated the length at first maturity (Simon et al. 2011).
Simon et al. (2011) developed a logistic maturity ogive for female Atlantic Wolffish based on the US NMFS surveys. They suggested a length at maturity of approximately 35 cm, which is similar to the Scotian Shelf estimates reported above. Given the uncertainty in estimating maturity of wolffish, Simon et al. (2011) adopted the same length of 50% maturity as McRuer et al. (2000) and Simpson and Kulka (2002), which is based on work by Templeman (1986) reported above, namely 51 cm.
Atlantic Wolffish are typically solitary except during pair formation in the spawning season. They have internal fertilization (Johannessen et al. 1993) and spawning can occur in shallow water (<150 m) in crevices and rock refuges, and also in deeper waters (150 to 200 m) (Saemundsson 1949 in McRuer et al. 2000). Little is known about spawning activities in deep waters. Off the coast of Newfoundland, spawning is believed to occur in the fall (Templeman 1984).
Atlantic Wolffish are iteroparous, with females producing a small number of eggs relative to other large-bodied teleosts. In one study, fecundity increased exponentially with fish length: the average number of eggs was 2,440 at 40 cm and 35,320 at 120 cm (Templeman 1986). Egg survival is probably high due to their large size (5.5 - 6.5 mm according to Bigelow and Schroeder 1953 in McRuer et al. 2000). In addition, the eggs adhere to the substrate and are guarded by the male until they hatch, which increases their survival (Keats et al. 1985).
Laboratory studies have shown that Atlantic Wolffish hybridize with Spotted Wolffish, a closely related species (Gaudreau 2009). However, there is no genetic evidence of hybridization in the wild (see McCusker and Bentzen 2008). The existence of hybrids is possible given that the ranges of the two species overlap, and this has been proposed by Luhmann (1954) on the basis of morphological characters.
The incubation period of the Atlantic Wolffish is unknown. However, in the Spotted Wolffish, the species most closely related to the Atlantic Wolffish, hatching is believed to occur after 800 to 1000 degree-days (Falk-Petersen and Hansen 2003). Newly hatched larvae are over 20 mm in size (Wiseman 1997 in Kulka et al. 2007) and remain close to the bottom until the yolk sac is absorbed. They then move to near-surface waters and drift with the current, but generally do not move far from where they were hatched (McRuer et al. 2000).
Growth is rapid in the initial years of life, but then slows considerably when the fish divert energy toward gonad development (Nelson and Ross 1992). In the Gulf of Maine, the average size of fish captured ranged from 4.7 cm at age 0 to 98.0 cm at age 22 (maximum age recorded in the study) (Nelson and Ross 1992). The maximum size observed by Templeman (1986) was 127 cm in males and 121 cm in females. According to Barsukov (in McRuer et al. 2000), the Atlantic Wolffish can reach up to 152 cm.
Generation time is defined by COSEWIC as the average age of parents of the current cohort:
G = A + 1/M,
where A is age at which 50% of females are mature and M is the instantaneous rate of natural mortality. From McRuer et al. (2002) data, a minimum A of 10 years would be calculated. An assumed M value for a fish that can reach a maximum age around 22 years would generally be 0.2. Generation time would then be approximately 15 years.
Atlantic Wolffish have been found in a wide range of water temperatures (from -1.5°C to 10°C) (Albikovskaya 1982, Beese and Kandler 1969 in Kulka et al. 2007), with concentrations in the middle of that range (Kulka et al. 2004). Dive observations suggest they do not tolerate brackish or fresh water (Kulka et al. 2004).
Adult Atlantic Wolffish do not move far. Templeman (1984) reported the results of a tagging study conducted between 1962 and 1966. A total of 398 Atlantic Wolffish were tagged and 20 individuals were recaptured. Most individuals were recaptured within a short distance of the original tagging site (approximately 8 km on average, all wolffish species combined). Short migrations have also been observed in the eastern Atlantic (Hansen 1958 and Jónsson 1982 in Templeman 1984) and off West Greenland (Riget and Messtorff 1988). However, migrations of several hundred km have been observed in the studies reported. Atlantic Wolffish can conduct short (few km) seasonal migrations between offshore waters and shallow waters (<120 m deep) for spawning (Nelson and Ross 1992). Eggs cannot disperse because they are deposited on the bottom. However, Kulka et al. (2004) showed that larvae and small juveniles were widespread in the upper water column, allowing for dispersal at that stage.
Templeman (1985) showed that Atlantic Wolffish feed primarily on invertebrates (85% of diet by volume) and, to a lesser extent, fish (15%). Most invertebrates consumed are whelks, sea urchins, hermit crabs, other crabs and scallops. Redfish was the main fish species eaten, though fish were a negligible part of the diet in the Maritimes Region (Simon et al. 2010). Recent data also indicate the importance of invertebrates (mostly crabs and echinoderms) in the diet (Simpson et al. 2011). Smaller Atlantic Wolffish consume a large proportion of invertebrates and a lower proportion of fish (Templeman 1985). As they mature, a higher proportion of fish are eaten.
There is little information on the predators of Atlantic Wolffish. However, juveniles have been found in the stomachs of Harbour Seals, Phoca vitulina (Andersen et al. 2004). In addition, Mikkelsen et al. (2002) found that the Atlantic Wolffish is an important prey species of Grey Seals, Halichoerus gripus, in the waters of the Faroe Islands. Although wolffishes generally account for only a small fraction of the diet of seals, it is estimated that four seal species (Harp Seal (Phagophilus groenlandicus), Hooded Seal (Crystophora cristata), Grey Seal and Harbour Seal) consumed close to 6000 t of wolffishes in 1996 in the Canadian Atlantic (Hammill and Stenson 2000). The Harp Seal is the most significant predator because of its high abundance. Wolffishes have also been found in the stomachs of Atlantic Cod (Saemundsson 1949 in McRuer et al. 2000, Simon et al. 2011), Atlantic Halibut (Hippoglossus hippoglossus) (Chabot pers. comm. 2010, Simon et al. 2011), Sea Raven (Hemitripterus americanus), Spiny Dogfish (Squalus acanthius), Longhorn Sculpin (Myoxocephalus scorpius), White Hake (Urophycis tenuis), and Haddock (Simon et al. 2011).
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