ASSESSING THE RISK OF CLIMATE CHANGE TO AQUACULTURE: a national-scale case study for the Sultanate of Oman

Understanding the risks that climate change poses on different culture systems in different locations is important to enable the design of targeted adaptation and resilience building actions. We present an aquaculture climate risk assessment framework, applied to the aquaculture sector of the Sultanate of Oman, that identifies the sensitivity and exposure of different components of the sector to climate change risk, that is also relevant and broadly applicable to many other regions around the world.

Aquaculture is a rapidly expanding component of global food security, and in 2018 overtook wild harvest fisheries in its contribution to global human food supply (FAO, 2020). Although growing in importance for world food security and economic development, aquaculture is susceptible to climate change.

“So it is important to assess the risks and challenges that climate change poses to aquaculture in order to implement targeted adaptation and resilience building actions to safeguard future productivity.”

In the Sultanate of Oman, the aquaculture sector is at an early stage of development with commercial production having grown modestly from 13 t in 1998 to 450 t in 2018 (FAO, 2017). However, the sector has been identified for major expansion within Oman’s national economic diversification programme to support economic development and food security in decades to come (MAFW, 2019).

The government plans for development of the aquaculture sector focus on coastal shrimp ponds, finfish sea cages especially for seabream, recirculating aquaculture systems (RAS) for groupers and salmon, and ponds and raceways for sea cucumber and the endemic abalone Haliotis mariae (MAFW, 2019; and see Figure 1).

However, Oman is situated in one of the hottest regions on earth, and climate change is progressively developing in the northwestern Indian Ocean and Arabian Gulf at the same time as the development of Oman’s aquaculture sector.

Here we present a climate risk assessment (CRA) of the aquaculture sector of Oman. It builds on the CRA introduced by the Intergovernmental Panel on Climate Change in 2014 as a means for quantifying climate change risks to linked ecological-economic systems.

Methods

In this CRA, the calculation of climate risk for aquaculture is based on four components:

• Thermal sensitivity, which compares the optimum growing temperatures of different species cultured, in relation to average sea temperatures characterizing each governorate;
• Flooding and storm surge exposure, the vulnerability to coastal flooding and storm surge of different culture types in different governorates;
• Low-oxygen hazard, associated with the likelihood of cultured species being exposed to low-oxygen water conditions, taking into account the culture methods; and
• Disease vulnerability, potential exposure to significant diseases (based on the number of diseases of concern reported for each species and the culture method used).

For each component, the risk index is calculated based on the sensitivity of each species cultured to the risk factor and the expected exposure to the risk in each governorate. A measure of overall climate risk – by species and governorate – is then calculated as the unweighted mean of the four components (Figure 2).

Table 1 summarizes the species included, along with their expected potential for development within the aquaculture sector of Oman, the main culture systems, and the governorates where these are either produced or are foreseen to be produced.

For each species, the sensitivity to thermal stress from climate change was assessed. Disease risk is incorporated into this CRA as it may increase with climate change due to two factors.

Results

Thermal sensitivity

The 19 aquaculture species that may be farmed in ambient conditions differ widely in maximum preferred temperatures (TP90), ranging from 21.44ºC in gilthead seabream to 29.77ºC in yellowfin hind (Table 2).

Between Oman’s coastal governorates, there is also variation in SST, which averaged over the year is warmer in northern than southern coastal sea areas. In combination, species differences in TP90 and spatial differences in SST are reflected in thermal safety margins for candidate species that vary considerably, from positive (ambient SST < species’ TP90, i.e. low thermal stress; shaded blue in Table 2 to highly negative (ambient SST > species’ TP90, i.e. high thermal stress; shaded red).

Exposure to flooding and storm surge

Shrimp culture is assessed as being at high risk from sea level rise and flooding, particularly in Al Batinah, Muscat and Ash Sharqiyah – the latter governorate important for current shrimp production.

This risk factor is low for species farmed in floating sea cages (seabreams, amberjacks, Asian seabass), and for the northern governorate of Musandam; the steep coastal topography and many deep sheltered bays (khawrs) appear to render Oman’s.

Hazard from low-oxygen levels

The hazard from low-oxygen levels in sea water was assessed as greatest (score 12 on scale 1–12) for fish species cultured in marine cages (seabreams, amberjacks, seabass, cobia), especially in southern governorates (Al Wusta, Dhofar) with coastal waters more likely to be impacted from hypoxic conditions.

However, most production for these species is envisaged further north where this risk factor is lower. For groupers reared in RAS, low-oxygen hazard is assessed as low owing to the controlled conditions, whereas for Atlantic salmon reared in RAS this hazard is assessed as intermediate owing to the active-swimming behavior and associated high oxygen demands.

Vulnerability to disease

The culture type ranking highest for disease vulnerability, was shrimp. This reflects the large number (9) of OIE listed diseases for Penaeus vannamei and P. monodon. In pond culture, where seawater is brought in, it is difficult to fully exclude disease from ponds; barriers or filters can be incorporated but completely excluding disease vectors remains challenging.

For the three amberjack species (2 OIE listed diseases), import of live broodstock is expected; some
import of juveniles is envisaged for grouper culture (3 OIE listed diseases for greasy grouper), which would increase risk of pathogen introduction.

Disease vulnerability is ranked low for seabreams with few OIE listed diseases, where production takes place in many different sea cages and is hence not highly concentrated.

Overall climate risk to aquaculture

Overall climate risk to aquaculture in Oman – combining thermal sensitivity, flooding exposure, low-oxygen hazard and disease vulnerability – is highest for shrimp culture (Table 3).

This is due to (1) high disease vulnerability, and (2) high exposure of coastal shrimp ponds to flooding or storm surge. Flooding exposure is high in Ash Sharqiyah where shrimp culture is being started; it is lower for Al Wusta but within this governorate, sites suitable to shrimp culture would typically be at low elevation and flood risk will depend on the exact location of each facility.

For Penaeus indicus, overall risk is scored lower than for P. vannamei and P. monodon due to a smaller number of OIE listed diseases, however as highlighted above, diseases in both other species have been investigated far more extensively, and P. indicus is impacted by the important white spot disease. Hence overall climate risk to P. indicus might be underestimated here.

“Overall climate risk is also high in amberjacks cultured in sea cages, due to (1) exposure to pathogens (with amberjacks being at risk from at least two OIE listed viral diseases) and (2) potential hazard from low-oxygen levels (amberjacks being active swimmers with high oxygen demands).”

Low-oxygen risk is higher in waters off Al Wusta, during the monsoon season impacted by the Arabian Sea oxygen minimum zone. However, flooding exposure to cage-farming is low. Of the three amberjack species, Japanese amberjack is at highest climate risk, owing to its cooler-water preferences and therefore higher thermal sensitivity if reared in cage conditions in Omani waters.

Low climate risk was recorded for the two grouper species, yellowfin hind and greasy grouper. They have been proposed for culture in RAS, which are inherently less impacted by ambient temperature or other environmental conditions.

Even so, both yellowfin hind and greasy grouper are well within their natural temperature ranges in Omani waters, and hence would experience little thermal stress if re-located outside. Moreover, the fully isolated, RAS conditions make exposure to pathogens less likely.

Omani abalone and sea cucumber aquaculture are characterized as low risk, partly due to these species being within natural temperature ranges, especially within the governorates of Dhofar and Al Wusta, respectively, where these species would be cultivated.

For aquaculture of Atlantic salmon in Oman, a fully controlled and isolated RAS system is proposed, which would render salmon production relatively independent from ambient temperature or other environmental conditions; this does, however, necessitate full temperature control given salmon’s cold-water requirements.

This also makes the risk from pathogen introduction low, provided original stock is safely sourced free of OIE listed diseases.

Conclusions

This aquaculture CRA, the first for Oman, demonstrates the application of a flexible framework that identifies climate risks to the aquaculture sector. Importantly the CRA identified the overall climate risk level for different species, culture types and governorates, and for each the predominant components of climate risk.

A significant finding was that the highest climate risk is for shrimp farming yet this is seen as a cornerstone for future aquaculture development in Oman. Key risks identified are (1) disease vulnerability and (2) exposure to flooding.

“Climate risk is also high for the species currently cultivated in greatest quantities in Oman – gilthead seabream (Table 3). It is here driven by (1) thermal sensitivity and (2) low-oxygen hazard, and less by storm surge exposure or disease risk.”

Alternative, technical option is the use of submersible cages (sunken to deeper, cooler waters) provided these are well aerated. Seasonal stocking of giltheads (part RAS and part net pen) may be another alternative to avoid the highest-risk periods.

For recirculating aquatic systems (RAS), climate risk is considered low (groupers) or fairly low (Atlantic salmon) (Table 3). This is due to the highly controlled culture conditions, which decouple these systems from natural environmental fluctuations (Soto et al., 2018).

Thus, thermal and low-oxygen related risks are low. Nevertheless, backup power systems are required as temperatures would soon be out of control if cooling failed in case of power shortages. Moreover, if RAS are situated close to sea they are still prone to inundation, and there is the need to manage risks from disease vulnerability.

“Screening-level risk assessment, such as carried out here provides guidance to scientists, resource managers and stakeholders on how climate change is expected to impact the physiology, life cycles and environment of aquaculture species and, ultimately, the way they are farmed.”

The study also highlights knowledge gaps in aquaculture research across a broad range of farming systems; outcomes from this assessment will focus attention towards the research required to underpin more detailed quantitative assessments of higher risk culture types, species and sites and thus more optimal allocation of human and operational resources.

Aquaculture production provides significant social, economic and nutritional benefits globally. The methods presented provide a broadly applicable, cost-effective and rapid approach not only to assess risk, but also to communicate risk to stakeholders and facilitate the necessary dialogue on pathways to adaptation – elements that make these methods relevant to many other regions around the world to build climate resilience in the global food chain.

This is a summarized version developed by the editorial team of Aquaculture Magazine based on the review article titled “ASSESSING THE RISK OF CLIMATE CHANGE TO AQUACULTURE: A NATIONAL-SCALE CASE STUDY FOR THE SULTANATE OF OMAN” developed by: GEORG H. ENGELHARD – International Marine Climate Change Centre University of East Anglia.
ELLA L. HOWES – International Marine Climate Change Centre; JOHN K. PINNEGAR-International Marine Climate Change Centre, University of East Anglia; WILL J.F. LE QUESNE -International Marine Climate Change Centre.
The original article, including tables and figures, was published on FEBRERO, 2022, through CLIMATE RISK MANAGEMENT.
The full version can be accessed online through this link: https://doi.org/10.1016/j.crm.2022.100416