Statistical indicators such as rising variance and rising skewness in key system
parameters may provide early warning of ‘‘regime shifts’’ in communities and populations.
However, the utility of these indicators has rarely been tested in the large, complex ecosystems
that are of most interest to managers. Crustacean fisheries in the Gulf of Alaska and Bering
Sea experienced a series of collapses beginning in the 1970s, and we used spatially resolved
catch data from these fisheries to test the predictions that increasing variability and skewness
would precede stock collapse. Our data set consisted of catch data from 14 fisheries (12
collapsing and two non-collapsing), spanning 278 cumulative years. Our sampling unit for
analysis was the Alaska Department of Fish and Game statistical reporting area (mean n for
individual fisheries ¼ 42 areas, range 7–81). We found that spatial variability in catches
increased prior to stock collapse: a random-effects model estimating trend in variability across
all 12 collapsing fisheries showed strong evidence of increasing variability prior to collapse.
Individual trends in variability were statistically significant for only four of the 12 collapsing
fisheries, suggesting that rising variability might be most effective as an indicator when
information from multiple populations is available. Analyzing data across multiple fisheries
allowed us to detect increasing variability 1–4 years prior to collapse, and trends in variability
were significantly different for collapsing and non-collapsing fisheries. In spite of theoretical
expectations, we found no evidence of pre-collapse increases in catch skewness. Further, while
models generally predict that rising variability should be a transient phenomenon around
collapse points, increased variability was a persistent feature of collapsed fisheries in our study.
We conclude that this result is more consistent with fishing effects as the cause of increased
catch variability, rather than the critical slowing down that is the driver of increased variability
in regime shift models. While our results support the use of rising spatial variability as a
leading indicator of regime shifts, the failure of our data to support other model-derived
predictions underscores the need for empirical validation before these indicators can be used
with confidence by ecosystem managers.