A synthesis of the early life history of the anglerfish, Lophius ...

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A synthesis of the early life history of the anglerfish 71 62°N 61 Division Vb 1000 m 200 m 60 Shetland Norwegian Deeps 59 Sub-area VI (West of Scotland and Rockall) Orkney Latitude 58 57 Rockall Plateau Outer Hebrides Sub-area IV (North Sea) Division IIIa (Skagerrak) 56 55 54 Sub-area VII 53 –16 –14 –12 –10 –8 –6 –4 –2 0 2 4 6 8 Longitude Figure 1. Main study area, showing relevant ICES areas and locations mentioned in the text. 10°E important target species. In Scotland, for example, anglerfishes were the second most important finfish landed in 1996 and 1997, in terms of total quayside value, whereas they were in sixth place in 1986 (source: The Scottish Office Agriculture, Environment and Fisheries Department). This change reflects both the high price commanded by anglerfishes and the reduced opportunities to exploit the depleted stocks of traditional demersal targets (e.g. cod, Gadus morhua; haddock, Melanogrammus aeglefinus; and whiting, Merlangius merlangus). Estimates of total international landings since 1950 from the area considered in this paper (Figure 1) are given in Figure 2. There has been a sharp increase in landings since the mid 1980s, corresponding to an increase in Scottish landings from the northern North Sea and west of Scotland. Landings from other areas and by other nations over this period have remained relatively small, with the percentage taken by Scottish vessels increasing from close to 50% in 1985 to a peak of 75% in 1996. There are no indications that this increase in landings reflects a corresponding change in the abundance of anglerfishes. Rather, it is more likely that this increase in landings has only been sustained by factors such as reduced discarding, technical improvements of gear and the expansion of the fishery into deeper waters to the north and west of Scotland (ICES, 2000). However, such developments cannot sustain a fishery indefinitely and decreased landings in 1997 and 1998 may be a warning sign. Preliminary management measures have been applied to anglerfishes; precautionary Total Allowable Catches (TACs) have been set for ICES Sub-areas VI (since 1986) and IV (since 1998). However, the development and implementation of an effective stock management Landings (tonnes) 40 000 30 000 20 000 10 000 0 1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 IIIa IV VI Total Figure 2. Estimated total international landings of anglerfishes (L. picatorius and L. budegassa) from the Skagerrak and Kattegat [ICES Division IIIa (........)], the North Sea [ICES Sub-area IV ( )] and West of Scotland and Rockall [ICES Sub-area VI ( )], 1950–1998. Figures for 1950–1972 are figures as officially reported to ICES; figures for 1973 to 1998 are taken from ICES (2000). ( =Total).
72 J. R. G. Hislop et al. strategy has been hindered by a lack of knowledge of the basic biology of anglerfishes. For example, little is known about when and where anglerfishes spawn in northern European waters and there is uncertainty about several key events during the first year of life. This ignorance can be attributed to the unusual spawning habits of Lophius. The eggs and larvae are pelagic. However, whereas most marine fish produce individual free-floating eggs that disperse over a wide range, anglerfish eggs are extruded in a buoyant, gelatinous ribbon that may measure more than 10 m25 cm (Prince, 1891; Fulton, 1898) and contain more than 1 000 000 eggs (Fulton, 1891). The highly clumped distributions of the eggs and newly emerged larvae – up to 95 000 larvae per 10 m 2 (O’Brien, 1986) – explains why conventional egg and larval surveys have provided very little information on the timing of spawning and the location of the spawning grounds. The early life history of L. piscatorius was the subject of three major reviews in the first part of the 20th century (Fulton, 1903; Bowman, 1920; Tåning, 1923). Fulton and Bowman dealt mainly with the North Sea, whereas Tåning also presented data from ichthyoplankton surveys of the oceanic waters of the northeast Atlantic, including the western seaboard of the British Isles. It was evidently unusual to catch female anglerfish on the point of spawning, although small numbers of females in an advanced stage of maturity were taken in the North Sea in February, May and July (Fulton, 1903). The few egg ribbons and isolated anglerfish eggs caught in the Northeast Atlantic were taken between February and early August. Bowman (1920) noted that Lophius eggs and larvae were taken only in the northern, i.e. deeper, parts of the North Sea and many of the post-larvae caught west of the British Isles were taken over or close to deep water (1000 m) (Tåning, 1923). Larval and post-larval stages (20 mm) were taken west of the British Isles in May, June and August (Tåning, 1923). Taken together, these pelagic records suggest that Lophius has a long spawning season. Although demersal anglerfishes >200 mm were widely distributed over the northern North Sea and were not uncommon on inshore grounds, very few small (
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