The viability of fish populations relies on healthy habitats where juveniles can spawn, feed and develop. A cornerstone of sustainable fisheries management, these habitats are facing increased pressure from coastal development, climate change, pollution and a number of other factors.
It means there is an urgent need for better tools to understand which habitats really matter for both juvenile and adult fish populations so they can be conserved and managed. However, there are a number of challenges around how the quality of juvenile habitats is measured.
To try and address this, members of the International Council for the Exploration of the Sea (ICES) Working Group on the Value of Coastal Habitats for Exploited Species (WGVHES) – including
Dr Benjamin Ciotti
from the University of Plymouth – undertook a comprehensive review to evaluate the approaches being used to assess juvenile habitat quality.
They reviewed almost 900 studies from the past five decades covering juvenile fishes, crustaceans, and molluscs in marine and estuarine systems, with the goal being to evaluate how current science assesses habitat quality.
The resulting study, published in the Biological Reviews journal, highlights that despite widespread recognition of the ecological importance of juvenile habitats, the majority of existing studies employed relatively few metrics.
Around 85% of the research focused on measuring juvenile abundance, typically using methods like net surveys or diver-based visual counts. While this provides some information on whether a habitat is being used by a fish species, it does necessarily mean they are thriving in these areas.
The working group has called for more research factoring in the growth and particularly survival of fish, as while approximately half of the studies incorporated growth indicators, only 16% included measurements of juvenile survival. Crucially, fewer than 10% of the studies attempted to directly assess how juvenile habitats contribute to adult populations, which is widely considered to be the best metric of juvenile habitat quality.
This narrow focus, the scientists say, highlights a major gap in the evidence needed to evaluate habitat quality which is in turn leading to a mismatch between policy needs and available science, with management decisions often relying on incomplete or indirect indicators.
Dr Benjamin Ciotti
