Graduate students do a lot of reading. And, sometimes, you stumble on a research article that is so obvious you wonder why you never thought about it before.
For me, one such article was, “Landscapes to Riverscapes: Bridging the Gap between Research and Conservation of Stream Fishes” coauthored by Kurt Fausch and his colleagues in 2002. I first read this article as an undergraduate, and it’s probably been assigned reading in no fewer than five other classes along my academic journey. Every time I read it I think two things. First, “duh”. Second, “why are we (still) ignoring these concepts in our management of fisheries?”
The take away message is that fish ecology is often not reflected in our design of research projects and management of fish populations. Seems like a major oversight, right?
In everyone’s defense, it’s really difficult, perhaps impossible, to cover all aspects of a species’ ecology when designing a research project. For example, we’re lucky if we can scrape together enough funding to run a project for 2-5 years. But, many fish species live much longer than that and are affected by processes that occur much less frequently (e.g., disease, rare weather events) or over very long time scales (e.g., climate change, evolution). So, we end up with a series of studies with important results, but results that many not be entirely appropriate for the species of interest. For example, a short-term study on the effects of floods on fish populations might conclude that they are catastrophic. But, if you look 10-50 years later, you might find that they are beneficial.
Likewise, scientific crews are often small, overworked, and under paid. We can only cover but so much area, and so we decide to sample a few hundred feet, maybe yards, of habitat. Or, we might use aerial maps to visualize entire watersheds. But, with these two approaches we’ve missed the spatial scale that is likely most important. Fish don’t stay put in one pool, or even a small stream segment. And, very often, they don’t move around the entire watershed. The scale that is probably most important, at least for trout, is measured in miles. But, sample crews can’t measure fish and habitat across miles of stream, and we certainly can’t use maps to document the fine-scale habitat features that are found in these stream segments.
The scary thing is that our data often lie to us, and we don’t know that we’ve collected information at the wrong temporal or spatial scale needed to answer the research question of interest. We could study the same population of fish for decades and never see movement. But then, suddenly, a slight increase in temperature or a little bit more rain, and you may see long-distance dispersal (this happens in populations of Arkansas darters, which seem to make long-distance movements, but only every 5-10 years after heavy rains). Or, we might study a species only during summer (which is common) and miss seasonal behaviors or changes in habitat use that correspond to different stages in the individual’s life cycle. And, if we do that, we may (and often do) falsely conclude that fish don’t move or make some other inaccurate statement about a species’ ecology.
Even more scary, these rare events and small-scale habitat features that we very often miss in our studies are some of the most important for fish populations. It’s the rare, long-distant movements that recolonize streams and connect populations. And, it’s the seasonal use of tiny areas of ground water upwelling or short-term occupancy of unique habitat features that fish use to spawn or survive thermal stress.
Though scientists are starting to realize the inadequacies of our studies (not to say we are fixing them, our hands are often tied), management hasn’t always kept up. For starters, managers’ hands are also tied. They can only work with the information they have and, as I’ve said, the information is often inaccurate or missing. But, sometimes, the protocols in place for protecting fish species need updating to better reflect improved information on species ecology- information that highlights the importance of considering different temporal and spatial scales in management plans.
Take for example Pennsylvania. In Pennsylvania waterways are given a designated use classification based on the aquatic species present. The streams I’m currently researching have different designated uses depending on the exact location, but include “Exceptional Value,” “High Quality Cold Water Fishes,” and “Migratory Fishes,” largely due to the presence of healthy trout populations. But, Loyalsock Creek itself has a designated use for ‘Cold Water Fishes’ indicating the river is used to propagate or maintain cold water species, including trout.
What’s the problem? This designation system emphasizes population size, which is a very reasonable approach when considering the data in hand and average conditions. Shanerburg Run is a high quality system because there are far more trout there than in Loyalsock Creek and, unlike Loyalsock Creek where summer temperatures far exceed trout thermal tolerance, Shanerburg Run can support trout all year. Further, evidence of wild trout in Loyalsock Creek has been limited because most sampling occurs in summer (when Loyalsock is too hot) and the system, which is a combination of deep pools, shallow riffles, and large boulders, is test for all fisheries sampling gear.
However, as we are learning from our telemetry study (and perhaps the anglers of Loyalsock already knew), Loyalsock Creek may be critical over-wintering habitat for a sub-set of brook trout. They don’t stay there all year, and it’s certainly only a small proportion of fish, but these nomadic individuals may be critical for sustaining brook trout population connectivity. As I talked about in my post last week, connectivity greatly improves population health by increasing genetic diversity and lowering the probability of population extirpation. So, protecting these fish may be disproportionately more important when considering conservation strategies.
Given this, are main stem rivers getting enough protection in brook trout watersheds? It’s hard to say. This is one case on one small scale with results that are still unfolding. But, it does highlight the need to think beyond “average” and consider how fish habitat use may change depending on the time and space scale you are considering.
Leave a Reply.