Large-scale climatic effects on traditional Hawaiian fishpond aquaculture.

Daniel Mccoy,Margaret A Mcmanus,Charles Young,Angela HiʻIlei Kawelo,Rosanna ʻAnolani Alegado,Kathleen C Ruttenberg,Brandon D’Andrea,KeliʻIahonui Kotubetey,Vanesa Magar

doi:10.1371/journal.pone.0187951

Abstract

Aquaculture accounts for almost one-half of global fish consumption. Understanding the regional impact of climate fluctuations on aquaculture production thus is critical for the sustainability of this crucial food resource. The objective of this work was to understand the role of climate fluctuations and climate change in subtropical coastal estuarine environments within the context of aquaculture practices in Heʻeia Fishpond, Oʻahu Island, Hawaiʻi. To the best of our knowledge, this was the first study of climate effects on traditional aquaculture systems in the Hawaiian Islands. Data from adjacent weather stations were analyzed together with in situ water quality instrument deployments spanning a 12-year period (November 2004 –November 2016). We found correlations between two periods with extremely high fish mortality at Heʻeia Fishpond (May and October 2009) and slackening trade winds in the week preceding each mortality event, as well as surface water temperatures elevated 2–3°C higher than the background periods (March-December 2009). We posit that the lack of trade wind-driven surface water mixing enhanced surface heating and stratification of the water column, leading to hypoxic conditions and stress on fish populations, which had limited ability to move within net pen enclosures. Elevated water temperature and interruption of trade winds previously have been linked to the onset of El Niño in Hawaiʻi. Our results provide empirical evidence regarding El Niño effects on the coastal ocean, which can inform resource management efforts about potential impact of climate variation on aquaculture production. Finally, we provide recommendations for reducing the impact of warming events on fishponds, as these events are predicted to increase in magnitude and frequency as a consequence of global warming.

Highlights

Over 400 million people depend upon fish protein as part of their daily diet [1]
The long-term variability of air temperature, wind speed, and rainfall data from Kāne’ohe Bay Marine Corps Air Base (KBMCB) and water temperature from MOKH1 was estimated from daily averages (Figs 2 and 3)
The records of air temperature, wind speed, and wind direction measurements from MOKH1 and KBMCB were consistent for these same periods (Fig 4)

Summary

Introduction

Over 400 million people depend upon fish protein as part of their daily diet [1]. While the yield of global capture fisheries has remained static since the 1950s due to overexploitation, the contribution of aquaculture is increasing dramatically, from 3.9% in 1970 to 36% in 2006 [2], overtaking wild-caught fish in 2014 [3]. During the evolution of an El Niño event, weakening equatorial trade winds cause a reversal in the atmospheric pressure gradient between the western and eastern Pacific, culminating in gradual movement of the warm pool eastward across the Pacific. This shift in equatorial conditions accounts for the main sources of regional year-to-year variability in weather and climate [6,7]. Mean water temperatures in Kāneohe Bay were not significantly different from the mean water temperature from March-December 2009 (26.5 ± 2.0 ̊C) during the week prior to the May and October fish kills (27.0 ± 0.5 ̊C and 28.4 ± 0.9 ̊C, respectively) (Table 3).

Objectives

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Results

Conclusion