Longfin eels (Anguilla dieffenbachii) are an apex predator in New Zealand freshwater ecosystems that, like anguillid species globally are in decline. One of the major challenges cited to their recovery is their uniquely slow growth rate. However, feeding trials demonstrate that longfin eels growth is comparable to other anguillids when sufficient food is available. In Aotearoa (New Zealand) diadromous migrations of galaxiid fish have declined 10-fold in the last 40 years owing largely to lowland habitat loss and land use intensification. The significance of this decline of a potentially significant food source in impacting the current state of the national longfin eel population has not been considered.
This presentation provides an overview of a recently initiated study to quantify the role of marine subsidies, namely galaxiid fish, in supporting diet and growth of longfin eels. We will present data from the Waituna Lagoon ecosystem – a nationally unique case study owing to the abundance of coastal wetland habitat for galaxiid spawning and rearing – quantifying the diet and growth of longfin eels in the presence of abundant galaxiid fish. We will outline future research directions to be taken over the next three years including using δ15N of archived otoliths to quantify marine subsidy and growth rate relationships from historic archived otolith samples. These results will be placed in the context of novel conservation opportunities for freshwater species; reinvigorating marine-freshwater connectivity.