Aspects of the biology of estuarine fish populations sampled from power station trash screens

Abstract

In the absence of previous investigations the present study considers fish populations in the Medway (England) Estuary; their type, composition and migration patterns. Seasonal growth of first-year plaice and flounder is also investigated. Fish were sampled monthly between 1973 and 1975 using power station trash screens as the quantitative sampling method. A total of 46,228 fish, 49 species and weighing 325.0 kg were taken. Monthly samples were dominated by sprats which, with 13 other species, formed more than 90 percent of the catch in most months. Based on seasonal distributions and length-frequency changes in consecutive months a model of fish migration patterns was constructed. In most cases emigration and immigration were separated by one or more months between spring and autumn, while in clupeoids they appeared to occur coincidentally during spring and summer.

Size composition and seasonal changes in abundance of juvenile sole, Solea solea, in the Severn Estuary and Inner Bristol Channel

“…The observation that the majority of sole caught within the Severn Estuary were less than 240 mm in length parallels closely the situation found by Van den Broek (1980) in the Medway Estuary. The three sole caught above 300 mm (345, 349, 400 mm) were almost certainly more than two years old.…”

Seasonal abundance, growth, feeding and age composition of flounder(platichthys flesus(l.)) populations of the severn estuary and bristol channel

“…The inflexion in the log • weight/log length curve marks a significant change in the weight-length coefficient from the higher values in the 0+ group (3.300-3.344) to the lower values (2.918-3.200) in the 0+ to 5+ age groups. These results are very similar to those recorded for flounders in the Medway estuary23 where the youngest 0+ class fish showed a weight-length coefficient of 3.370 compared to values of 3.023-3.095 for older fish of the 1+-3+ age classes for the 1+-5+ age groups in 1972/1973 and the highest value of 3.200 in 1975/1976, suggesting very favourable conditions for growth in the latter season, which saw exceptionally high water temperatures and low discharge rates.For each of the seasons from 1972-1976 the regression equations for log • weight on log • length for the 0+ class fish were as follows: 1972-1973 N = 435 Log W = -2.346 + 3.344 Log L r = 0.981 1973-1974 AT = 819 Log W = -2.401 + 3.340 Log L r = 0.991 1974-1975 TV = 1226 Log W = -2.344 + 3.300 Log L r = 0.902 1975-1976 N = 1619 Log W = -2.398 + 3.330 Log L r = 0.981 For the 1H-5+ age classes the corresponding equations were: 1972-1973 TV = 780 Log W = -1.939 + 2.918 Log L r = 0.900 1973-1974 N = 616 Log W = -2.010 + 3.028 Log L r = 0.989 1974-1975 N = 1376 Log W = -2.121 + 3.010 Log L r = 0.991 1975-1976 N = 1369 Log W = -2.221 + 3.200 Log L r = 0.987…”

“…21 ' 22 Investigations on this species based on power station samples from the river Medway have also been reported. 23 …”

Age composition, growth, movements, meristics and parasites of the whiting, Merlangius merlangus, in the Severn Estuary and Bristol Channel

“…The minimum (38 mm) and approximate mean standard length (53 mm) at the time whiting were first caught in the Inner Severn Estuary correspond to total lengths of 45 and 62 mm. These lengths are similar to that recorded for the first whiting immigrants in the Tamar Estuary (Hartley, 1940) and Medway Estuary ( Van den Broek, 1980). They are greater, however, than those recorded for the 0 + of several other abundant marine teleosts in the estuary which as adults grow to a relatively large size (Claridge & Potter, 1983, 1984.…”