ICES mar. Sei. Symp.. 196: 183-189. 1993 Swimming speeds of marine fish in relation to fishing gears Pingguo He He, P. 1993. Swimming speeds of marine fish in relation to fishing gears. - ICES mar. Sei. Symp., 196: 183-189. Swimming ability plays a vital role in the survival of fish in terms of catching a prey and escaping from a predator or a fishing gear. Knowledge of how fish swim and how well they can swim is very important in the design and operation of selective and energy- conserving commercial fishing gears, and in fisheries resource assessment through better understanding of selectivity and efficiency of survey trawls. This paper summar­ izes recent findings of swimming performance in marine fishes and discusses how a change in swimming ability due to biological and environmental conditions and how a change in trawl operation can influence the size selectivity of a trawl. Special attention is paid to commercially important species, including mackerel (Scomber scombrus), herring (Clupea harengus), cod (Gadus morhua), and saithe (Pollachius virens). Pingguo He: Fisheries and Marine Institute, Memorial University of Newfoundland, PO Box 4920, St John’s, Newfoundland, Canada A1C 5R3. Introduction L.), herring (Clupea harengus L.), jack mackerel (Tra­ ck urns japonicus (Temminck and Schlegel)), mackerel, Many contributions have been made since the 1920s on or Atlantic mackerel (Scomber scombrus L.), Pacific how, and how well, fish swim (see Beamish, 1978; mackerel (Scomber japonicus Houttuyn), and saithe Videler and Wardle, 1991). However, our understand­ (Pollachius virens (L.)). ing of the swimming ability of commercial marine fishes and their swimming behaviour near fishing gears is very limited. Yet knowledge of fish behaviour has become Swimming speeds: mackerel as increasingly important in present-day fisheries. Com­ an example mercial fishing operations have come to such a stage that operators are required only to catch certain species of The Atlantic mackerel is by far the most completely particular sizes, using specified fishing gears at the speci­ studied fish species in respect to swimming performance. fied location and time. Fisheries scientists conducting Here mackerel is taken as an example to define the survey fishing operations use the same fishing gear in a swimming speeds of fish. Recorded swimming speeds of vast area, hoping for a constant and known efficiency mackerel range from a minimum of 0.4 L s ' 1 (body and selective performance of the gear over space and lengths per second, 0.32 m specimen) to a maximum of time. 18 L s” 1 (0.31 m specimen). Figure 1 summarizes swim­ Fish swimming speeds have been reviewed by Blaxter ming speeds, endurance, body attack angle, and the use (1969), Beamish (1978), and more recently by Videler of swimming muscles at different speeds. and Wardle (1991), and underwater observations of fish The Atlantic mackerel has no swimbladder and is behaviour near towed trawls by Wardle (1983, 1986, heavier than seawater, therefore it has to swim con­ 1989). This paper summarizes recent findings concern­ stantly in order to generate lift to keep itself from ing the swimming capacity of commercial marine fishes, sinking. The minimum swimming speed (U mjn) of 0.4 L combined with those from field observations of fish s“ 1 was recorded when the fish was swimming at a body swimming near fishing gears, to explore the selectivity of attack angle of 27° (He and Wardle, 1986). Without a trawl codend and how it is affected by the way fish swim body tilt, mackerel must swim at a minimum speed of 1L and their swimming ability. s” 1. The preferred swimming speed (Up) of mackerel Species mentioned in the text are bluefin tuna (Thun- was between 0.9 and 1.2 L s- 1 when cruising around a 10 nus thyrtnus L.), cod, or Atlantic cod (Gadus morhua m diameter annular tank (He and Wardle, 1988). Mack- 183 direction of swimming predicted 7.5 L s 1 swimming speed is called the maxi­ mum prolonged swimming speed (U mp) and the range of speeds between U ms and U mp is called prolonged swim­ ming speeds. The white muscle as well as the red muscle is used for swimming at the prolonged speeds. Speeds beyond U mp are called burst speeds, at which Swimming speed (L/s) only the white muscle effectively contributes to the Inset: energy required for swimming. The white muscle oper­ mackerel swimming with a body attack angle ates anaerobically and its energy reserve can be depleted in a matter of seconds at burst speeds. The maximum swimming speed (Umax) of mackerel ever recorded is 18 L s -1, which is very close to the predicted U max from white muscle contraction time of 19 L s-1 at 12°C (Wardle and He, 1988). iustained prolonged ’***——-_____ speeds speeds [ | burst speeds h' The maximum sustained swimming red m. red + w hitël I white muscle | 35 L ■ I ■ I ■ I , I , I , I , I . 1 ■ I ■ speed 0 2 14 6 T8 10 12 14 16 18 20 Umin ] Mp |Ums lUmp I Umax The maximum sustained swimming speed (Ums) marks Swimming speed (L/s) the upper limit of the sustained speeds (without leading Figure 1. Swimming speeds (in body lengths per second) of the to exhaustion) and the lower limit of the prolonged Atlantic mackerel (Scomber scombrus L.) from the lowest to speeds (leading to exhaustion). It has been demon­ the highest value recorded, plotted against endurance. Use of strated by monitoring muscle activities in 0.15 m long different types of muscles at different speed ranges is indicated. jack mackerel that the red muscle only is used at swim­ Inset: mackerel swimming with a body attack angle at speeds ming speeds up to U ms of 6.2 L s-1, while the white below Up. See text for explanation. muscle joins in at speeds beyond U ms (Xu, 1989). The force generated from a muscle is related to the erel swim at speeds below U p only when space is re­ cross-sectional area of the muscle (Ikai and Fukunaga, stricted in a laboratory tank (He and Wardle, 1986) or 1968). It is thus not surprising that pelagic fish species when the light level is very low (<10 6 lux) (Glass etal., possessing thick red muscle achieve a higher U ms. For 1986). Many neutrally buoyant species can stop swim­ example, herring and saithe each of 0.25 m length have a ming; their minimum swimming speed is therefore equal maximum lateral red muscle cross-sectional area of 0.85 to 0. Mackerel can swim between 1 and 3.5 L s~1 indefi­ nitely without leading to exhaustion (He and Wardle, V) E Saithe: 1988). This speed range is called the sustained swimming v> M •, um =1.40 L° w speeds, at which mackerel cruise voluntarily in large E tanks and at sea, and during migration and feeding. When the swimming speed exceeds 3.5 L s-1, limited wI TO endurance leads to exhaustion. This 3.5 L s" is called c0) the maximum sustained swimming speed (U ms). In prac­ aj 3C/5 um*<m/s) Inset: pelagics tice, U ms is the maximum swimming speed with an V) endurance equal to or greater than 200 min. Ea 0.9 E For swimming speeds greater than U ms, the higher the aj>< speeds (U), the shorter the endurance (E). In mackerel, 5 the relationship between E (in min) and U (in L s” 1) can 0.1 0.2 0.3 0.4 0.5 0.6 be expressed in semi-log regression as (He and Wardle, Body length, L (m) 1988); LogE = -0.96U x 5.45. The maximum swim­ Figure 2. The maximum sustained swimming speed in relation ming speed involving power from the red muscle may be to body length of pelagic species (solid curve) and demersal predicted in the same way as Wardle (1975) did with the species (dashed curve). Letter symbols are: M - Atlantic white muscle. The fastest red muscle contraction time is mackerel, Scomber scombrus, 11.7°C, H - herring, Clupea about twice that of the white muscle in mackerel (He et harengus, 13.5°C (He and Wardle, 1988); and J - jack mack­ al., 1990). These authors predicted that at swimming erel, Trachurus japonicus, 19°C (Xu, 1989). Solid diamonds: saithe, Pollachius virens, 14.4°C (He and Wardle, 1988). Inset: speeds above 7.5 L s ' 1, the red muscle will become pelagic species; BT - bluetin tuna, Thunnus thynnus, of 2.44 m ineffective as an energy source for swimming, owing to length with a predicted U ms of 2.10 m 1 s (see text for expla­ simultaneous contraction of muscle on both sides. This nation). 184 and 0.55 cm2 respectively (He, 1986). Likewise, herring Larger fish can swim longer at the same speed in m s“1 has a U ms of 1.06 m s_1 compared with 0.89 m s-1 for or they can swim faster at the same endurance. For saithe, both at around 14°C. example, a 0.50 m long saithe can swim for 30 min at 1.25 The maximum sustained swimming speed (U m!,, in m m s_1, while a 0.25 m saithe can only swim for 2 min at s ' 1) increases with an increase in fish body length (L, in the same speed of 1.25 m s” 1 or can only swim at 0.95 m m) in both saithe and small pelagics (mackerel, herring, s” 1 for the same endurance of 30 min (Fig. 3c). Pelagic and jack mackerel) (Fig.