Effects of Human Influences and Natural Persistence on Low Streamflow Changes in the United States

International audienceAccurate assessment of low streamflows is important to the management of water supply, ecological conditions in streams, and protection of water quality. This study compares observed trends in low streamflow across the conterminous U.S. at near-natural (Hydroclimatic Data Network-2009) stream gages to trends at stream gages which have experienced substantial basin alteration (Agricultural, Regulated, and Urban), while accounting for the natural persistence present in low-flow time series. This work provides insight into regional climate-related trends in low streamflows and changes driven, in part, by human activities. Trends were tested for low 1-, 3-, and 7-day streamflows, number of zero-flow days, and annual deficit metrics at 2,482 U.S. Geological Survey stream gages across the conterminous U.S. For all time periods tested (50, 75, and 100 years through 2015), higher low streamflows over time were consistently observed throughout much of the northeastern quadrant of the conterminous U.S., as were lower flows in the southeastern and northwestern U.S. Reference gages with minimal human impacts generally indicated lower low-flow conditions over time for much of the U.S. In agricultural basins, trends predominantly indicated higher low-flow conditions over time which may be associated with increased precipitation and activities related to annual row crop cultivation. Trends in regulated basins were generally toward higher low flows, lower annual deficits, and fewer days of zero flow, though results were less regionally coherent. Geographic distributions of trends at urban gages were very similar to those for the reference gages but generally had a greater percentage of significant upward trends in low streamflows, fewer days of zero flow, and decreases in annual deficits which may be attributed to urban landscape features and patterns of water use and waste-water discharge that can increase base flow

Unitary development plan Issues paper

SIGLEAvailable from British Library Document Supply Centre- DSC:OP/LG-5889 / BLDSC - British Library Document Supply CentreGBUnited Kingdo

The current status and management of South Africa’s chondrichthyan fisheries

Chondrichthyans (sharks, skates, rays and chimaeras) are captured in many marine fisheries. Management and research efforts directed at chondrichthyan fishing are often neglected because of low product value, taxonomic uncertainty, low capture rates, and harvesting by multiple fisheries. In South Africa’s diverse fishery sectors, which include artisanal as well as highly industrialised fisheries, 99 (49%) of 204 chondrichthyan species that occur in southern Africa are targeted regularly or taken as bycatch. Total reported dressed catch for 2010, 2011 and 2012 was estimated to be 3 375 t, 3 241 t and 2 527 t, respectively. Two-thirds of the reported catch was bycatch. Regulations aimed at limiting chondrichthyan catches, coupled with species-specific permit conditions, currently exist in the following fisheries: demersal shark longline, pelagic longline, recreational line, and beach-seine and gillnet. Limited management measures are currently in place for chondrichthyans captured in other South African fisheries. Catch and effort dataseries suitable for stock assessments exist for fewer than 10 species. Stock assessments have been attempted for five shark species: soupfin Galeorhinus galeus, smoothhound Mustelus mustelus, white Carcharodon carcharias, spotted ragged-tooth Carcharias taurus, and spotted gully Triakis megalopterus. Fishery-independent surveys and fishery observer data, which can be used as a measure of relative abundance, exist for 67 species. Compared with most developing countries, South African shark fishing is relatively well controlled and managed. As elsewhere, incidental capture and bycatch remain challenges to the appropriate management of shark species. In 2013, South Africa’s National Plan of Action for the Conservation and Management of Sharks (NPOA-Sharks) was published. Implementation of the NPOA-Sharks should help to improve chondrichthyan management in the near future.Keywords: bycatch, fisheries management, shark fisheries, shark trade, stock assessmen