Some information on offshore bottom longline fishery in the southern Adriatic Sea (GFCM Geographical Sub-Area 18) Ungaro Nicola #, Marano Giovanni #, De Zio Vito #, Pastorelli AnnaMaria #, Rositani Lucio # Abstract The offshore bottom longline fishery in the Southern Adriatic Sea (GFCM GSA 18) mostly targets the European hake (Merluccius merluccius) and is carried out on the continental slope bottoms. The fishery is characterized by highly variable levels of activity according to the time periods and weather conditions. Nevertheless, fishermen consider the economic yield of this fishery as very interesting because of catch rate and quality, as it mainly consists of large-sized fish specimens. Some of the target species are also exploited by other fisheries such as bottom trawling. The possible increase of the fishing mortality of the older cohorts within the fish population is thought to be because of the bottom longline selectivity and efficiency. The monitoring of this fishery is therefore relevant for fishery management in the area, due to the gear features and catches. Key-words: artisanal fishing; demersal fisheries; longlining; offshore; Merluccius merluccius; MED, Adriatic Sea, Southern 1. Introduction Offshore bottom longline fishery in the Southern Adriatic Sea could be considered as a "small scale activity" due to the small number of vessels and fishermen involved. Moreover, the importance of the fishery is very low if compared with the demersal trawl fishery. Nevertheless, the social-economic impact of the offshore bottom longline fishery could be important at local level due to the high commercial value of the target species. Offshore bottom long-lining mainly targets the large-sized European hakes (Merluccius merluccius). Other high-priced species, such as scorpionfish, gurnards and blackspot seabream, are also caught contributing to the success of the fishing trips. 2. The fishing activity Offshore bottom longline fishery is carried out mostly on the continental slope off the southern Adriatic Sea (GFCM GSA 18). Both soft and rocky areas are exploited. The fishing activity targeting the hake occurs on muddy bottoms from 200 to 400 m depth as a rule, while scorpionfish, gurnards and blackspot seabream are mostly caught at 150-350 m depths on mixed bottoms (De Zio et al., 1998). The number of boats involved in this fishery is quite low, and a rough estimate of 20-30 Italian vessels could be made for the basin. With regard to the Italian fleet, most of the boats are located in the harbours of Mola and Monopoli (both within the maritime department of # Laboratorio Provinciale di Biologia Marina - Molo Pizzoli (Porto), 70123 Bari Italy. Email: biologia.marina@teseo.it 98
Bari). Tonnage and engine power of the vessels are mostly between 10 and 15 t (GRT) and 75 and 150 kw respectively. Moreover, some boats from other maritime districts (i.e. Sicily) occasionally operate in the area. Offshore bottom long-lining is carried out all year round. However, due to the fishing gear and characteristics of the activity (good sea conditions are is needed as a rule) the number of fishing trips at sea is highly variable and 20-30 trips/boat per year can represent an indicative estimation. The duration of each trip is from two to four days, depending on the weather conditions. The standard offshore bottom longline is generally 3500 m long, and the number of hooks ranges from 500 to 700 (Table 1). Each vessel can use more than one bottom longline set during the fishing trip. Details on the gear can be found in Pietrucci and Antolini (1990). Table 1. Some features of the offshore bottom longline used in the GSA 18. Hook type and size Mustad 4-7 Mainline length 3500 m Mainline material and diameter Multifilament, 5.0 mm Monofilament, 2.0 mm Branch line length 1.8 m Branch line diameter 1.20 mm Distance between branch line 5.5 m Baits Sardine, squids The increasing use of the line hauler has been observed in the last 10 years, and some tests on full automation systems have been carried out (Romanelli and Tarulli, 2002). 3. The fishery yield and catch composition The fishery mostly targets the hake, which represents between 40 and 70 of the total catch weight (De Zio et al., 1998; Romanelli and Tarulli, 2002). Other species caught are considered as "secondary targets" when these are marketable or valuable, or as by-catch when they are less valuables or discards. These species are reported in Table 2. Table 2. Secondary target and by-catch species from offshore bottom longline fishery. Conger conger (European conger) Galeus melastomus (Blackmouth catshark) Helicolenus dactylopterus (Blackbelly rosefish) Hexanchus griseus (Bluntnose sixgill shark) Lepidopus caudatus (Silver scabbardfish) Mustelus mustelus (Smooth-hound) Pagellus bogaraveo (Blackspot(=red) seabream) Phycis blennoides (Greater forkbeard) Phycis phycis (Forkbeard) 99
Polyprion americanus (Wreckfish) Raja spp. (Rays and skates) Scorpaena elongata (Slender rockfish) Scorpaena scrofa (Red scorpionfish) Squalus acanthias (Picked dogfish) Trigla lucerna (Tub gurnard) Trigla lyra (Piper gurnard) The secondary species fished with noteworthy yields are C. conger (10-20), H. dactylopterus (5-10), P. bogaraveo (2-4) and T. lucerna (1-2) (Figure 1). Helicolenus dactylopterus 4 Others 6 Raja spp. 2 Phycis blennoides 1 Pagellus bogaraveo 1 Conger conger 11 Merluccius merluccius 75 Figure 1. Species weight composition in bottom longline fishery catch in the southern Adriatic Sea; year 1992 (modified from De Zio et al., 1998). The quantity of landed catches could be estimated at 300-500 kg/vessel/fishing trip (De Zio et al., 1998). The C.P.U.E (effort unit measure is 100 hauled hooks) for hake ranges between 5 and 7 both in number and weight (kg); the overall C.P.U.E. figures (all species) varies between 10 and 20 in number and 10 and 30 kg (Romanelli and Tarulli, 2002). The incidence of discarded species mostly refers to G. melastomus (blackmouth catshark), which can constitute an important percentage on deeper bottoms only (Romanelli and Tarulli, 2002). The catch of all species in offshore bottom longline fishery mostly consists of large-sized individuals (above the sexual maturity length). The length of the hake specimens is larger than 25-30 cm TL as a rule (Figure 2) (De Zio et al., 1998). 14 12 10 8 6 4 2 Merluccius merluccius (L.) Southern Adriatic Sea: bottom long-line fishery 0 30 36 42 48 54 60 66 72 78 84 90 96 Figure 2. Length-frequency distributions of M. merluccius from bottom longline fishery in the southern Adriatic Sea; year 1992 (modified from De Zio et al., 1998). 100
The offshore bottom longline fishery in GSA 18 interacts with other activities and mainly with bottom trawl fishery. In fact, for some species exploited by both bottom long-lining and trawling, the fishing areas and resource availability overlap, although the fishing effort deployed by trawling is much higher. The Mediterranean hake is the main target species for both the activities but the fraction of population exploited by the two fisheries is quite different (Ungaro et al., 2003); in fact, trawl fishery mostly catch juveniles (first age and length cohorts) while bottom long-lining mainly exploits larger sizes (spawners) (Figure 3). Similar results have also been reported for other species (Figure 4) (Ungaro et al., 1999). 25.00 20.00 Southern Adriatic hake catch by gear type 15.00 Merluccius merluccius 10.00 5.00 0.00 0 4 8 12 16 20 24 28 32 36 40 44 48 52 56 60 64 68 72 76 80 Trawling Bottom long-line Figure 3. Length-frequency distributions of M. merluccius caught by bottom trawl and longline in the southern Adriatic Sea (Ungaro, unpubl.). 35 30 25 20 15 10 5 0 Southern Adriatic bluemouth scorpionfish catch by gear type Helicolenus dactylopterus 4 6 8 10 12 14 16 18 20 22 24 26 28 30 rete Trawling a strascico palangaro Bottom long-line Figure 4. Length-frequency distributions of H. dactylopterus caught by bottom trawl and longline in the southern Adriatic Sea (modified from Ungaro et al., 1999). 4. Discussion and Conclusions The offshore bottom long line fishery carried out in the GSA 18 is characterized by high variability rate of the activity depending on time periods and weather conditions. Nevertheless, fishermen regard the economic yield of the fishery as very interesting because of C.P.U.E and quality of the catches. Moreover, most of the boats practicing bottom longlining have the possibility to use the drifting longline for large pelagic fish (swordfish and 101
tunas) as an alternative according to the season, the resource availability and the economic profit. The bottom longline catches mainly consist of large-sized specimens, so the possible increase in fishing mortality on older cohorts of the stocks due to the gear selectivity and efficiency, and the depletion of the spawning biomass could affect the population of some species. This is particularly the case of the Mediterranean hake, a very important resource for the whole fishery sector in the southern Adriatic Sea (Ungaro et al., 1993; Ungaro and Marano, 1996). In fact, European hake size in the catch of both trawl and longline overlap from 20 to 40 cm length, which is the sexual maturity length range for the species (Ungaro et al., 2003). The monitoring of bottom longline fishery, due to this gear features and catches, would therefore also seem a relevant issue for fishery management in the area. 5. References De Zio V., Ungaro N., Vlora A. & Strippoli G. (1998) Lo stock di nasello del Basso Adriatico: struttura demografica e rendimenti di pesca della frazione catturata con palangaro di fondo. Biol. Mar. Medit., 5 (2): 128-135. Pietrucci A. & Antolini B. (1990) Rilancio della pesca con il palangaro di fondo. Gazzettino della Pesca, 4: 32-38. Romanelli M. & Tarulli E. (2002) Mechanization of fishing operations by fixed gears: report on tests performed by two automation systems for bottom longlines in the southern Adriatic and northeastern Ionian Seas. Thalassia Salentina, 26: 81-111. Ungaro N., Rizzi E., Marano G. (1993) Note sulla biologia e pesca di Merluccius merluccius (L.) nell'adriatico pugliese. Biologia Marina, 1: 329-334. Ungaro N. & Marano G. (1996) Considerations on the hake stock of the South-Western Adriatic Sea. FAO Fish. Rep., 533 (Suppl.): 97-100. Ungaro N., Martino M., Di Turi L. & Strippoli G. (1999) Sulla demografia di alcune specie ittiche demersali catturate da differenti attrezzi. Biol. Mar. Medit., 6 (1): 623-626. Ungaro N., Mannini P. & Vrgoc N. (2003) The biology and stock assessment of Merluccius merluccius (L.) in the Adriatic Sea: an historical review by geographical sub-areas. Acta Adriatica, 44(1): 9-20. 102