Domestic Ballast Water - Survey data
1 Scope
The aim of project 406293 is to improve understanding of the risks posed by domestic ballast water (BW) discharges in New Zealand (NZ) and the practicality, feasibility, and costs of associated management activities, such as BW exchange and treatment systems. The knowledge gained through this project will assist the management of NZ’s marine domestic pathways.
These analyses focused on work-package 1B: Characterising domestic BW flux and management.
2 Objectives
The objectives of the analyses were to determine the following :
the uptake and discharge behaviour (including volumes, frequencies, residence times, and locations) for domestic BW in the context of coastwise voyage operations;
the application (if any) of domestic BW management approaches by this fleet, including coastwise exchange, onboard treatment, internal BW management (within-ship ballast transfers);
the status of BW treatment systems during coastwise voyages in NZ (i.e., are they present, are they used, explanations for not using them, etc.).
3 Methods
The domestic BW survey was conducted using a stratified survey approach. Based on the analysis of AIS data, vessels were stratified based on their registration, voyage profile, and type. The survey aimed to census international and New Zealand-registered vessels that operate exclusively in the country.
The survey of international vessels was conducted over three months (April and June 2022).
The electronic version of the survey is available online.
4 Results
4.1 Number of vessels per category and registration
The survey was sent out by the BNZ Intelligence and Targeting team to 281 vessels and had a response rate of ~78% (219 vessels, Table 1).
| vessel_category | n | percent |
|---|---|---|
| Cargo | 105 | 47.9% |
| Container | 70 | 32.0% |
| Fishing | 2 | 0.9% |
| RoRo | 18 | 8.2% |
| Tanker | 24 | 11.0% |
| Total | 219 | 100.0% |
A total of 49 distinct domestic vessels completed the survey (Table 2). Fishing (65.3%) and “Other” (26.5%) vessels dominated the sample.
| vessel_category | n | percent |
|---|---|---|
| Cargo | 1 | 2.0% |
| Container | 1 | 2.0% |
| Fishing | 32 | 65.3% |
| Other | 13 | 26.5% |
| RoRo | 2 | 4.1% |
| Total | 49 | 100.0% |
4.2 BW capacity
Fifty-one percent of the surveyed domestic vessels had the capacity to carry BW (Figure 2 (a)). Most “Other” vessels (77%) had no BW capacity.
Most international registered vessels had BW capacity (Figure 2 (b)), the only exception being three fishing and three cargo vessels (Figure 2 (a)).
Domestic registered vessels did not have BW treatment systems, while 79% of the internationally-registered vessels had treatment systems (Figure 2 (b)).
4.3 BW management during voyages
Domestic vessels did not manage BW during voyages, whereas most international vessels treated BW onboard and a small proportion exchanged BW offshore (Figure 3).
4.4 Treatment types
The most popular treatment type across vessel categories (61.2%) was filter + UV, followed by Filter + Electrolysis (28.8%, Figure 4).
4.5 Reasons for not managing BW
Reasons for not managing BW taken up in NZ waters are listed in Table 3. The most common reason was that the vessel had no treatment system installed.
| Why do you not manage ballast water taken up in New Zealand waters? | n |
|---|---|
| No answer provided | 1 |
| No system installed | 5 |
| Not enough time to conduct ballast water exchange on voyage from New Plymouth to Nelson | 1 |
| System was not installed at time, understands regulations allow untreated discharge | 1 |
| Vessel not fitted with BWTS and not able to do exchange due to short voyage and distance from nearest land | 1 |
| Vessel will not discharge ballast between NZ ports | 1 |
4.6 Uptake and discharge behaviour
The majority of domestic (72%) and internationally-registered (59%) vessels with BW capacity declared never to have taken up BW within NZ waters (Figure 5 (a)). In particular, most domestic fishing and international RoRo vessels had never taken up BW within NZ.
Out of the domestic vessels that declared taken up BW, only three subsequently discharged them in NZ waters (Figure 5 (b)). Most international vessels (55%) discharged NZ sourced BW in other locations within NZ (Figure 5 (b)).
4.7 Ballast water movement
Vessels that indicated they had previously taken up BW within NZ waters (i.e., within 12 NM) and had subsequently discharged it in other locations within NZ were prompted to provide copies of their BW logbooks. Specifically, we asked respondents to provide copies of up to the last ten NZ-based voyages. Eighty-four vessels provided copies of their logbooks; however, subsequent screening of these documents indicated that 45 did not contain relevant information, resulting in 39 unique vessels (Table 4) Cargo and container vessels represented 79.5% of the total number of vessels. Fishing, Roro and Tanker vessels were underrepresented, with only one, two and five vessels, respectively (Table 4).
| vessel_category | n | percent |
|---|---|---|
| Cargo | 16 | 41.0% |
| Container | 15 | 38.5% |
| Fishing | 1 | 2.6% |
| RoRo | 2 | 5.1% |
| Tanker | 5 | 12.8% |
| Total | 39 | 100.0% |
A total of 1,471 individual BW movements were recorded for these 49 vessels, with 87.6% recorded for cargo and container vessels (Table 5).
| vessel_category | n | percent |
|---|---|---|
| Cargo | 846 | 57.5% |
| Container | 443 | 30.1% |
| Fishing | 44 | 3.0% |
| RoRo | 72 | 4.9% |
| Tanker | 66 | 4.5% |
| Total | 1471 | 100.0% |
Of the total BW movements recorded, 51.2% and 43.8% corresponded to uptake and discharges, respectively Table 6. A small proportion (5%) were internal transfers and were not considered in subsequent analyses.
| activity | n | percent |
|---|---|---|
| Discharge | 645 | 43.8% |
| Internal transfer | 73 | 5.0% |
| Uptake | 753 | 51.2% |
| Total | 1471 | 100.0% |
Table 7 shows the number of distinct vessels, itineraries and tanks for each vessel category and BW movement activity.
| vessel_category | activity | vessels | itineraries | tanks | records |
|---|---|---|---|---|---|
| Cargo | Discharge | 16 | 29 | 209 | 413 |
| Cargo | Uptake | 16 | 29 | 211 | 433 |
| Container | Discharge | 15 | 25 | 90 | 149 |
| Container | Internal transfer | 6 | 12 | 45 | 73 |
| Container | Uptake | 15 | 30 | 116 | 221 |
| Fishing | Discharge | 1 | 8 | 2 | 19 |
| Fishing | Uptake | 1 | 9 | 2 | 25 |
| RoRo | Discharge | 2 | 2 | 5 | 32 |
| RoRo | Uptake | 2 | 2 | 8 | 40 |
| Tanker | Discharge | 5 | 7 | 27 | 32 |
| Tanker | Uptake | 5 | 7 | 27 | 34 |
4.8 BW movements volume
Median BW movement per tank volume was 540 m3 and ranged between 0.5 and 10,100 m3. Median volume was comparable among activity types (uptake, discharge and transfer), but varied considerably between vessel categories (Figure 6). The lowest volumes were for fishing and RoRo vessels and the highest for tanker, cargo and container vessels.
4.9 BW movements rate
Median BW transfer rate was 4.7 m3 h-1 and ranged between 0.02 and 33.6 m3 h-1. Transfer rate was comparable among activity types (uptake, discharge and transfer), but varied considerably between vessel categories. The highest were recorded for cargo, container and RoRo and the lowest for fishing and tanker vessels. (Figure 7).
4.10 Proportion of treated BW movements
All domestic vessels’ BW movements were untreated (Figure 8). Most international-registered vessels BW’s movements were treated, during intake and discharge, although some were untreated and of unknown treatment status.
4.11 Activity maps per vessel
The maps in Figure 9 show all BW movements (excluding internal transfers) by different vessel categories and movement types (uptake and discharge) at the vessel-itinerary level, i.e. combining all tanks involved in a given BW movement. Major ports, including Tauranga, Wellington, Mardsen Point, Gisborne and Nelson, were discharge hotspots, with 75, 37, 36, 29 and 21 discharges recorded. Eighteen discharges were recorded at coastal locations outside ports and only six at offshore locations (all from a single fishing vessel).
The most significant uptake location was the Port of Auckland, with 100 uptakes recorded, followed by Tauranga (67), Timaru (55) and Lyttelton (42). There were 12 coastal and 12 offshore uptakes.
Apart from New Plymouth, there were no BW movements on the West Coast.
4.12 Distance to the coast
Distance to the nearest coastline for individual activity points is shown in Figure 10. The largest and smallest distances were recorded for fishing and RoRo vessels. Distance patterns were similar for BW uptake and discharge.
4.13 Residency times in ballast tanks
Onboard residency times were calculated for each vessel, itinerary and tank combination by subtracting the discharge start time from the uptake end time, representing the minimum time interval onboard a given tank as a conservative estimate of residency. Tanks discharges without corresponding intake records were excluded from the calculations.
Median BW residency time was 200 hours and ranging between 5 and 1,054 hours. Residency times were shortest for RoRo and longest for fishing vessels (Figure 11)
4.14 Time intervals between BW discharges
Intervals between BW discharges were calculated at the vessel-itinerary level by subtracting the previous discharge time from each discharge record. Vessel-itinerary combinations without records of last discharge were excluded from the calculations. Time intervals between BW discharges within the itineraries are shown by vessel category in Figure 12. On average, BW were discharged every 40 hours within a give itinerary, but this time ranged between 10 minutes and ca. one month (Figure 12). The time interval between discharges was longest for fishing vessels and shortest for Cargo.
4.15 Number of discharges per itinerary
On average vessel discharged BW 1.7 times per itinerary, up to a maximum of five times (Figure 13). RoRo discharged BW more times per itinerary (2.5 times) than other categories (ca. 1.7 times).
4.16 Activity maps at the itinerary level
The maps below show uptake and discharge activity for all vessel itineraries recorded, by vessel category (Figure 14 to Figure 18). Points were mapped using the start latitude and longitude of individual movements. Points are scaled to BW exchange volume.
Figure 14 shows nine itineraries undertaken by a single fishing vessel around the South of the South Island, including near offshore islands. Several BW movements, including discharge and uptake, were recorded within each itinerary, including ports (Timaru and Lyttelton), and coastal and offshore locations. BW movement volumes were relatively small (3 - 51 m3 , Figure 14).
Seven itineraries were recorded for tanker vessels (Figure 15) undertaken by five vessels. Most of these were inter-island voyages and included BW movements at major ports, including Tauranga, Wellington, Nelson, Mardsen Point, Dunedin, New Plymouth, Lyttelton, Napier and Timaru. No offshore movements were recorded for tanker vessels. The volume of the BW movements was relatively large (mean 1,958 m3, range = 60 - 15,821, Figure 15).
Thirty-five itineraries were identified for cargo vessels (Figure 16). These included BW at 13 major ports on both islands and one coastal location. Volume was relatively large (mean = 6,406 m3, range = 9 - 14,598 m3 , Figure 15).
Figure 17 shows 30 itineraries undertaken by 15 vessels. BW movements were recorded in eleven domestic ports, several coastal locations, and Sidney (itinerary 29, uptake and discharge not shown). BW movement volume ranged between 90 and 7,103 m3 (average 351 m3, Figure 17).
Only two itineraries were identified for RoRo vessels, both for voyages undertaken by the inter-island ferries across the Cook Strait (Figure 18). Each itinerary included BW movements at Queen Charlotte Sound, Cook Strait, Wellington, Picton, and Tory Channel (Figure 18). BW movement volume ranged between 1 and 1,334 m3 (mean = 448 m3).
4.17 Activity maps for untreated water only
The maps below show the uptake and discharge of untreated (or “Unknown”) movements of recorded itineraries by vessel category (Figure 14 to Figure 18). Points were mapped using the start latitude and longitude of individual movements. Points are scaled to BW exchange volume. Points are colour coded by tank ID and the shape mapped to activity type (i.e. discharge or uptake).
4.18 Untreated movements maps
4.19 Network analyses
4.20 Network centrality and Degree
A node’s centrality measures the node’s importance in the network. The degree of a node is the number of its adjacent edges.
5 Summary
While nearly half of the domestic fleet does not have BW capacity, most internationally-registered vessels do.
Domestic vessels do not treat BW because they do not have treatment systems, whereas most international vessels treat BW onboard, mainly using filters, plus UV or electrolysis.
Most domestic (72%) and internationally registered (59%) vessels with BW capacity declared never to have taken up BW within NZ waters.
Only 6% of all surveyed domestic vessels (three out of 49) declared to discharge BW within NZ waters.
Most international vessels (55%) with BW capacity declared to have taken up NZ-sourced BW and discharged them within NZ, representing 22% of all surveyed vessels.
Fishing and RoRo discharge relatively smaller volumes than other vessel categories.
Tankers discharge a large volume of BW at a relatively lower discharge rate.
Major ports were identified as discharge and uptake hotspots.
No BW activity was recorded on the West coast apart from New Plymouth.
Apart from ports, most discharges were at coastal locations, generally <10 km to the coast. An exception was a single fishing vessel uptaking and discharging small volumes at offshore locations.
Residency times were generally >4 days, except for RoRos (inter-island ferries) that had short residency time (<10 h)
Discharges generally occur ca. twice per itinerary at every 40 hours.