Rosanna Milligan

Environmental variability and biodiversity of megabenthos on the Hebrides Terrace Seamount (Northeast Atlantic)

We present the first remotely operated vehicle investigation of megabenthic communities (1004–1695 m water depth) on the Hebrides Terrace Seamount (Northeast Atlantic). Conductivity-temperature-depth casts showed rapid light attenuation below the summit and an oceanographic regime on the flanks consistent with an internal tide, and high short-term variability in water temperature, salinity, light attenuation, aragonite and oxygen down to 1500 m deep. Minor changes in species composition (3–14%) were explained by changes in depth, substratum and oceanographic stability, whereas environmental variability explained substantially more variation in species richness (40–56%). Two peaks in species richness occurred, the first at 1300–1400 m where cooler Wyville Thomson Overflow Water (WTOW) mixes with subtropical gyre waters and the second at 1500–1600 m where WTOW mixes with subpolar mode waters. Our results suggest that internal tides, substrate heterogeneity and oceanographic interfaces may enhance biological diversity on this and adjacent seamounts in the Rockall Trough.

A Scientific Basis for Regulating Deep-Sea Fishing by Depth

The deep sea is the worlds largest ecosystem, with high levels of biodiversity and many species that exhibit life-history characteristics that make them vulnerable to high levels of exploitation. Many fisheries in the deep sea have a track record of being unsustainable. In the northeast Atlantic, there has been a decline in the abundance of commercial fish species since deep-sea fishing commenced in the 1970s. Current management is by effort restrictions and total allowable catch (TAC), but there remain problems with compliance and high levels of bycatch of vulnerable species such as sharks. The European Union is currently considering new legislation to manage deep-sea fisheries, including the introduction of a depth limit to bottom trawling. However, there is little evidence to suggest an appropriate depth limit. Here we use survey data to show that biodiversity of the demersal fish community, the ratio of discarded to commercial biomass, and the ratio of Elasmobranchii (sharks and rays) to commercial biomass significantly increases between 600 and 800 m depth while commercial value decreases. These results suggest that limiting bottom trawling to a maximum depth of 600 m could be an effective management strategy that would fit the needs of European legislations such as the Common Fisheries Policy (EC no. 1380/2013) and the Marine Strategy Framework Directive (2008/56/EC).

High resolution study of the spatial distributions of abyssal fishes by autonomous underwater vehicle

On abyssal plains, demersal fish are believed to play an important role in transferring energy across the seafloor and between the pelagic and benthic realms. However, little is known about their spatial distributions, making it difficult to quantify their ecological significance. To address this, we employed an autonomous underwater vehicle to conduct an exceptionally large photographic survey of fish distributions on the Porcupine Abyssal Plain (NE Atlantic, 4850 m water depth) encompassing two spatial scales (1–10 km2) on and adjacent to a small abyssal hill (240 m elevation). The spatial distributions of the total fish fauna and that of the two dominant morphotypes (Coryphaenoides sp. 1 and C. profundicolus) appeared to be random, a result contrary to common expectation but consistent with previous predictions for these fishes. We estimated total fish density on the abyssal plain to be 723 individuals km−2 (95% CI: 601–844). This estimate is higher, and likely more precise, than prior estimates from trawl catch and baited camera techniques (152 and 188 individuals km−2 respectively). We detected no significant difference in fish density between abyssal hill and plain, nor did we detect any evidence for the existence of fish aggregations at any spatial scale assessed.

Disentangling habitat concepts for demersal marine fish management

Fishing and other anthropogenic impacts have led to declines in many fish stocks and modification of the seabed. As a result, efforts to restore marine ecosystems have become increasingly focused on spatially explicit management methods to protect fish and the habitats they require for survival. This has led to a proliferation of investigations trying to map ‘habitats’ vulnerable to anthropogenic impacts and identify fish resource requirements in order to meet conservation and management needs. A wide range of habitat-related concepts, with different uses and understandings of the word ‘habitat’ itself has arisen as a consequence. Inconsistencies in terminology can cause confusion between studies, making it difficult to investigate and understand the ecology of fish and the factors that affect their survival. Ultimately, the inability to discern the relationships between fish and their environment clearly can hinder conservation and management measures for fish populations. This review identifies and addresses the present ambiguity surrounding definitions of ‘habitat’ and habitat-related concepts currently used in spatial management of demersal marine fish populations. The role of spatial and temporal scales is considered, in addition to examples of how to assess fish habitat for conservation and management purposes.

The Effect of Parasitic Infection by Hematodinium SP. on Escape Swimming and Subsequent Recovery in the Norway Lobster, Nephrops Norvegicus (L.)

Tail flip escape swimming was measured in the Norway lobster, Nephrops norvegicus (Linnaeus, 1758) up to cessation and following 4 hours recovery, and was compared with that of lobsters infected by the parasitic dinoflagellate Hematodinium sp. Swimming in uninfected lobsters comprised around 65 high-power flips in Phase 1 and a variable number of less powerful flips in Phase 2. Lightly-infected lobsters executed fewer flips in Phase 2, and heavily-infected lobsters produced only a few weak flips. Following 4 hours recovery uninfected lobsters produced 84.3% of the flips produced initially, due to a smaller number of Phase 2 tail flips. Infected lobsters showed less recovery, proportional to the severity of infection. The metabolic basis of the two-phase swimming pattern and the reduced performance during infection by Hematodinium is discussed. Our findings have implication for the catchability of uninfected and infected N. norvegicus, especially on fishing grounds where the fishing effort is high.

A Deeper Perspective: 5 Years of The Delos Project (Portuguese)

The Deep-ocean Environmental Long-term Observatory System (DELOS) was installed in Block 18 Angola in February 2009, and therefore celebrates its 5th anniversary in February 2014. The two DELOS platforms are located 16km apart in 1,400m of water depth. One is within 50 metres of subsea facilities, and the second is 16km from any sea floor infrastructure. Each platform comprises two parts: - a sea floor docking station that is deployed on the sea floor at the start of the monitoring program and remains for the 20 year project duration; and a number of observatory modules that are designed to perform specific environmental monitoring functions. Each observatory module has enough battery and storage capacity for autonomous operation for 12 months. Towards the end of the 12 month deployment period each platform requires ROV (Remotely Operated Vehicle) intervention to recover observatory modules to the surface for service, calibration and data offload. DELOS has already provided the scientific community with a unique long-term dataset to study the natural environmental conditions in the deepwater of the Atlantic Ocean. The data collected so far has provided a unique opportunity to examine the spatial and temporal variability of physico-chemical conditions and biological communities. Studies to-date have shown, for example, a direct correlation between the physico-chemical conditions (temperature, salinity etc.) and the fish communities present at the two sites. Based on the results already collected by the project, the scientific community has strongly advocated the further development of paired, deep-water observatories in other regions of the World’s oceans. This paper will chart the successes, and challenges, of the DELOS project to-date, examine some of the data collected during the first 5 years, and discuss the need for continued, long-term observations of the deep ocean both offshore Angola and elsewhere.

Long Term Deepwater Environmental Monitoring Off Angola - Data Management Strategy

In early 2009, two Deep-ocean Environmental Long-term Observatory Systems (DELOS) were installed in around 1,400m water depth in Block 18, Angola. The intention is that they will provide a unique long-term (25 year) dataset of deep-ocean variability. Each station consists of a fixed platform structure into which serviceable modules containing oceanographic, acoustic and camera equipment are placed. One monitoring station is located near to subsea infrastructure, and the other is located at the same depth but distant from, and upstream of, any oil industry activities. This far-field platform also has a sediment trap module. This will enable both long term natural and anthropogenic changes in the physical, chemical and biological environment to be identified and investigated. The data will also allow an understanding of the pace of recovery from unforeseen impacts and provide a linkage between marine biodiversity and climate change. An international scientific steering committee initially developed the DELOS concept and specified the equipment. It now oversees the research associated with data interpretation. The modules are recovered approximately every twelve months, and the data downloaded, batteries changed and the equipment serviced before being returned to the seabed. This paper will discuss the pros and cons of the intermittent data collection and how the data are managed and interpreted, including sharing with our Angolan partners.