On food preferences of the Adriatic hake, Merluccius merluccius (L.)
Abstract
The trawling data collected during the »Hvar« Fishery Biological Expedition, mostly in the open Adriatic, at depths ranging from 20 to 382 m and at a mean depth of 125 m, in 1948 and 1949, showed a wide and continuous distribution of hake in the Expedition area. The data completed, to a large extent, earlier very incomplete knowledge on hake distribution in the Adriatic.
During the Expedition the hake was recorded at depths ranging from 20 to 382 m and at a mean depth of 126 m. These depths are almost equal to the Expedition trawling depths and are not in disagreement with the generally known depth preferences of the hake.
Within the Expedition area larger catches of the hake were obtained at greater depths. The highest population density was recorded in the Jabuka Pit and southwards, as well as along the north-eastern edge of the south Adriatic pit.
During the Expedition rather small hake were caught, 40.2% of the catches contained only individuals smaller than 40 cm and only 21.6% contained individuals of 60 cm and more.
The length range in individual hake catches was mostly rather wide (> 20 cm). The catches from greater depths showed wider length ranges than those from lesser depths.
The ratio of the length of the hake at first maturity to the asymptotic length (Lm/L∞ ) gave values of 0.36 and 0.41 (data of K i r i n č i ć and L e - p e t i ć, 1955, Ž u p a n o v i ć, 1968, and of the »Hvar« Expedition used), these being lower than those recorded in gadiforms from other seas (B e - v e r t o n and H o l t, 1959) and that found in the eastern Spanish hake (L a r r a ñ e t a, 1970).
A review of the data on food composition in the Adriatic hake showed that the rather small hake from the »Hvar« Expedition area exceeding 16 cm and showing a modal length of 27.5 cm fed mainly on pelagic fish (the sardine and anchovy) and bathypelagic fish (the mackerel, bogue and horse mackerels), (K a r l o v a c, O., 1959b). These data are in agreement with the data for the shallower northern Adriatic (P i c c i n e t t i, C. and G. P i c c i- n e t t i M a n f r i n, 1971) and those for the eastern Spanish coast (L a r r a- n e t a, 1970). In contrast, according to the data of J u k i ć (1975), the hake caught in the open central Adriatic, at depths ranging from 110 to 262 m and at a mean depth of 176 m, took mainly bathypelagic and benthic fishes from which none was found to be predominant.
The hake preyed on the sardine in the shallower part of the »Hvar« Expedition area (at a mean depth of 102 m). It had also to feed on other fishes recorded in the food of the hake mainly in shallower waters (at greater depths the hakes mostly had everted stomachs as shown by O. K a r l o v a c, 1959b). At depths exceeding those sampled during the food composition study by O. K a r l o v a c (1959b) the hake might have had different food preferences or perhaps no marked preferences at all. The differing data on the hake food composition given by J u k i ć (1975) might be due to difference in the trawling depths between the two series of observations.
The rather small hake (mean length of 28.5 cm) from the »Hvar« Expedition area (shallower part) fed on small sardines (mean length of 13.7 cm), (from the data of O. K a r l o v a c, 1961).
Data on the horizontal distribution of the fish species analysed from the point of the hake food preferences, in the »Hvar« Expedition area, partly studied earlier, showed a localized distribution of the sprat, in the shallowest waters (mean depth 69 m), (M u ž i n i ć, 1973b) and a distribution limited to the deepest waters of the area (mean depth 194 m) in Glossanodon leioglossus (V a l.). The other six species, i.e. Sardina pilchardus (W a l b.), Engraulis encrasicolus (L.), Boops boops (L.), Trachurus mediterraneus mediterraneus (S t d r.), Spicara smaris (L.) and S. maena flexuosa (R a f.), were recorded in rather shallow waters of the Expedition area of mean depths ranging from 89 to 106 m and showed a discontinuous distribution, due to the Jabuka Pit.
Trachurus trachurus (L.) and Argentina sphyraena L. occurred at greater and similar mean depths, 144 and 145 m, and had a continuous horizontal distribution in the Expedition area.
Scomber scombrus L. was found at a mean depth of 124 m (almost equal to the mean Expedition trawling depth) and showed a discontinuous horizontal distribution in the investigated area as shown earlier (M u ž i - n i ć, 1973a).
An analysis of the distributional data for the hake on one hand and the prey fish species on the other in the »Hvar« Expedition area showed that the hake had a horizontal distribution wider than that of any of the other fishes considered, but especially of Sprattus sprattus (L.), Sardina pilchardus (W a l b.), Engraulis encrasicolus (L.), Boops boops (L.), Trachurus mediterraneus mediterraneus (S t d r.), Spicara smaris (L.) and S. maena flexuosa (R a f.). None of these species could, therefrom, have an importance for the hake feeding in the whole Expedition area.
From the data on the hake food composition and the comparative distributional data on the species it appears that Sardina pilchardus (W a l b.), Sprattus sprattus (L.) and Engraulis encrasicolus (L.) may be the prey species preferred by the haike only in shallower waters. The hake seems to prefer mackerel in sommewhat deeper waters. The hake showing a preference for mackerel is probably larger. In contrast, Trachurus and Spicara species, as well as Argentina sphyraena L. might not be the preferred prey of the hake. However, more behavioural data are needed when considering these predator-prey relations.
