New Zealand longfin eel

Description

The New Zealand longfin eel (Anguilla dieffenbachii) is a species of freshwater eel that is endemic to New Zealand. It is the largest freshwater eel in New Zealand and the only endemic species the other eels found in New Zealand are the native shortfin eel (Anguilla australis), also found in Australia, and the naturally introduced Australian longfin eel (Anguilla reinhardtii). Longfin eels are long-lived, migrating to the Pacific Ocean near Tonga to breed at the end of their lives. They are good climbers as juveniles and so are found in streams and lakes a long way inland. An important traditional food source for Māori, longfin eels numbers are declining and they are classified as endangered, but over one hundred tonnes are still commercially fished each year. The easiest way to identify the longfin eel is by the length of its fins: the dorsal (top) fin is about two-thirds the length of the body and starts significantly further towards the head than the anal (bottom) fin. In the shortfin eel the fins are of similar length. When a longfin eel bends its loose skin wrinkles distinctively inside each bend, where a shortfin eel's skin is smooth. A longfin's mouth extends past its eyes, further than a shortfin's. Female longfin eels are larger and longer-lived than males. Males average 66.6 cm but reach up to 73.5 cm in length, with an average age of 23 years (12-35 years). Females are considerably larger, ranging from 73-156 cm with an average length of 115 cm. Females attain an age of 20 to 60 years before migrating to sea to breed. Longfin eels in the North Island migrate at a younger age and thus have faster generation times. Determining longfin sex is difficult as their sexual organs are not determined until they are over 45 cm in length. The only method to determine longfin eels sex is through internal examination and only becomes easy to distinguish when the eels mature and migrate. Anguilla dieffenbachii is endemic species to New Zealand, widely distributed through the country's lakes and rivers, including the Chatham Islands. Longfin eels are often found great distances inland (up to 361 km) along fresh waterways and in high country lakes which are connected to the sea. Aiding in their inland distribution is their climbing ability in elver (juvenile) stage, under 12 cm in length. These migration events frequently coincide with increased temperate, water flow and low light conditions.