Comparative angler catch rates of native versus alien piscivorous fish in an invaded river fishery.

Abstract

Recreational angling is a major introduction pathway for large-bodied alien fishes into freshwaters, where the fish are released to enhance angling success and increase angler satisfaction, despite this often resulting in invasive populations. There is a thus a need to understand the role of these alien species in angler catches to enable more informed risk-based decisions to be made on future releases. In England, the invasive, piscivorous pikeperch Sander lucioperca has been present in rivers since the 1960s. Anglers target invasive pikeperch in fisheries where the native piscivorous pike Esox lucius is also present; this includes two rivers in the lower Severn basin, western England (main River Severn and Warwickshire Avon). To assess the contributions of invasive pikeperch to angler catches, the aim here was to compare their catches with those of native pike in the lower Severn basin in relation to angling effort and methods, abiotic conditions, and fish size. In 307 angling sessions across 16 anglers where at least one fish was captured, 428 pike and 266 pikeperch were captured. In a sub-set of data from six anglers who submitted catch returns that included non-capture sessions, 78 % of sessions resulted in the capture of at least one pike or pikeperch. Catch rates of pike were significantly higher than pikeperch in the main River Severn but not the Avon. Captured pike were significantly larger than pikeperch, but pikeperch were larger relative to the maximum size each species reaches in England. Lures generally captured more pike than any other method, with these fish tending to be smaller than those caught on other methods; these patterns were not evident in pikeperch. Both species were captured across a broad range of river flow conditions (Q6 to Q99). Only 19 % of successful angling sessions resulted in the capture of both species, suggesting some species selectivity by anglers. These results emphasise that alien fish species can provide important angling resources in recreational fisheries, although management decisions on future introductions should still consider their ecological risks.