![Sample our Environment & Agriculture journals, sign in here to start your access, latest two full volumes FREE to you for 14 days]({"type":"image" , "src" : "/sda/5934/TOC-Subject-Sample-2021-Environment-Agriculture.jpg"})
Migrating adult freshwater eels, Anguilla australis Richardson and A. dieffenbachii Gray, were examined during the autumnal migration from the Makara Stream (1971–73), Lake Onoke (1971, 1972) and Lake Ellesmere (1972, 1974–80). Males of A. australis migrated from the Makara Stream at a mean length of 465 mm and from Lake Onoke at a mean length of 447 mm. The difference between the mean lengths at migration of A. australis males from Lake Ellesmere between 1972 (mean 443 mm) and 1980 (mean 425 mm) were significantly different. Females of A. australis migrated from the Makara Stream, Lake Onoke, and Lake Ellesmere at mean lengths of 737, 764, and 615 mm respectively.
Aging was by examination of burnt otoliths. Males of A. australis from each area migrated after spending an average of 14 years in fresh water. A. australis females migrated from the Makara Stream at an average age of 19 years, from Lake Onoke at 23 years, and from Lake Ellesmere at 24 years. A. dieffenbachii males and females were larger and older at migration than A. australis of the same sex. Males of A. dieffenbachii from the Makara Stream migrated at a mean length of 623 mm after spending an average of 23 years in fresh water; females may attain a large size before migration. A. dieffenbachii females migrated from the Makara Stream at a mean length of 1063 mm and from Lake Ellesmere at 1156 mm; ages ranged from 25 to 60 years.
There was a higher proportion of male to female A. australis in Lake Ellesmere and the Makara Stream than in Lake Onoke. In Lake Ellesmere the high percentage of migrating males (83–98%) recorded each year between 1972 and 1980 showed a reversal of the sex ratio from that reported earlier. In the Makara Stream there was a higher proportion of male to female A. dieffenbachii (17: 1), and in Lake Ellesmere female A. dieffenbachii outnumbered males (11: 1).
Migrating A. australis males from Lake Ellesmere were slightly heavier than those from the Makara Stream and Lake Onoke. Computed weights of A. australis females of the same length from each area were similar. Migrating A. dieffenbachii were heavier than A. australis migrants of the same length.
Changes in the length‐frequency and sex composition of migrating A. australis eels in Lake Ellesmere are coincident with extensive commercial eel fishing. These changes are probably related to the selective fishing for eels longer than 380 mm in the non‐migrant population.
