Abstract
Habitat restoration efforts in the upper San Francisco Estuary, including the Sacramento-San Joaquin Delta, California, move forward, despite a paucity of information on the environmental requirements of many targeted species. The endemic delta smeltHypomesus transpacificus, protected under the federal Endangered Species Act, is a primary focus of those efforts despite uncertainties regarding many aspects of its relationship with the estuary’s physical and biotic resources. Here we use time-series data from 4 trawl surveys and data on environmental attributes collected from throughout the delta smelt’s distribution to identify ranges of conditions acceptable to delta smelt for each of 5 environmental attributes: water-body type, temperature, turbidity, salinity, and prey availability. Low turbidity and elevated water temperatures render a large portion of the estuary seasonally unsuitable for delta smelt. Within areas in which water quality is suitable, patterns of delta smelt occurrences indicate that habitat is found in subregions where channels of intermediate depth adjoin shallow water. In certain subregions, conditions are inadequate for at least one of the environmental attributes for periods up to several months. We suggest a habitat-restoration strategy that can achieve adequate habitat conditions for delta smelt regardless of through-Delta flow levels, and which can be carried out at a number of locations, but not necessarily the same locations, during each life stage.
Highlights
It is a common understanding among conservation planners that the need for reliable knowledge regarding the habitat requirements of imperiled species frequently outstrips available relevant data (Kareiva et al 1998, Johnson et al 1999, Reed et al 2006)
The affinity analyses for subregions of the upper estuary showed significant differences that were generally consistent between delta smelt life stages (Table 4, and Fig. S1 in the Supplement)
The analyses confirm that habitat requirements for delta smelt vary by life stage and that the upper San Francisco Estuary exhibits diverse and fluctuating environmental conditions that influence habitat quality
Summary
It is a common understanding among conservation planners that the need for reliable knowledge regarding the habitat requirements of imperiled species frequently outstrips available relevant data (Kareiva et al 1998, Johnson et al 1999, Reed et al 2006). Descriptions of habitat requirements are inferred from species occurrence data, combined with supposition regarding resource requirements. How do resource managers employ limited data to draw inferences regarding. We answer those questions with a case study of the imperiled delta smelt Hypomesus transpacificus. We describe an analytic approach that draws from available survey data on delta smelt and the dynamic and degraded estuarine ecosystem that supports it. The identity of its Publisher: Inter-Research · www.int-res.com
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